Can I somehow Re-enlist with a 90% disability rating if none of my disabilities hinder my ability to deploy or train in any way?

The standards of medical fitness are the same on active duty or in the reserve component - you either meet them or you don't. If you don't meet one of the standards, then it may or may not be waiverable, depending on what it is. So, there should be no difference about your eligibility from either recruiter.

Keep in mind though that the standards of medical fitness for enlisting (or reenlisting) are more stringent than the standards of medical fitness for retention. You may have a condition that won't allow you to enlist, but if you are currently serving, wouldn't disqualify you from further service. So yes, it makes perfect sense that they wouldn't allow you in with a condition that you had before you were discharged. IF you had reenlisted within 12 months of discharge, then the enlistment standards wouldn't have applied. After 12 months, you have to meet the same medical standards as a fresh recruit.

As to a medical waiver taking away your disability - No, it won't (well, not automatically). You cannot collect VA disability at the same time as collecting a military paycheck. If you go back onto active duty, then any disability payment you have will be suspended for the duration of your active duty service. If you join the reserve component, then you won't receive a disability payment during drills, annual training, schools, etc., but you will still receive it while your not performing military duty.

Back to it being taken away. You were given a disability rating by the VA for the impact your disabling items from your military service would have on your future. If you reenlist and receive a waiver to enlist despite the disability, it doesn't make the disability go away. If on the other hand, you receive a waiver because the disability is not as limiting as the medical records state - Yes, that could affect your future VA rating.

I said "not automatically" because it's not like the Army will send a notice to the VA stating that your herniated discs aren't as limiting as your records indicate. However, when you are initially given a VA rating, buried in the packet you received should be an overview of when the VA will reevaluate your disability rating. Generally, the VA will do a reevaluation of your disabilities in the first two to five years after your initial rating - UNLESS you were granted a "permanent" rating on a disability. The reevaluation can be a records review or they may schedule your for a follow-up C&P exam if, based on your disability, there is a likelihood that it would improve over time.

This is where the "disconnect" could come in with the VA. Your records are going to be known to the VA (they'll pull the most current records when they do a reevaluation). If that 90% rating was because your herniated disc was so severe that it had a major impact, frequently had a moderate impact, etc., then the examiner would rightly question how you were able to reenlist with such a condition.

Bottom line - a disability rating from the VA, regardless of what it is (with one exception - if you were granted an Individual Unemployability rating), will not by itself prevent you from reenlisting - it is entirely dependant on the standards of medical fitness.

However, looking at the standards of medical fitness (DODI 6130.03), a "History of lumbar disc pathology, including, but not limited to, bulges, herniations, protrusions, and extrusions associated with symptoms, treatment, or limitations of activities of daily living or a physically active lifestyle, in the previous 24 months or any history of recurrent symptoms" (section 6.16h) is a disqualifying condition for which you would require a medical waiver.
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* DODI 6130.03 Volume I - Medical Standards for Military Service: Appointment, Enlistment, or Induction - https://www.esd.whs.mil/Portals/54/Documents/DD/issuances/dodi/613003_vol1.PDF
* AR 40-51 (Standards of Medical Fitness) - https://armypubs.army.mil/epubs/DR_pubs/DR_a/ARN37720-AR_40-501-002-WEB-4.pdf

90% but it doesn’t effect your deployability?

On the surface I have to be honest on how odd that sounds.

The AD response was expected because the medical readiness expectation for AD is higher. The Guard recruiter is being outwardly optimistic but it’s not for him to decide. He left it up to the board.

Feel free to apply but I think you may be better served looking at some other way to serve. Plenty of ways to get out there and serve other than the military

To get in you must complete an Army Chapter 2 Initial procurement physical from MEPS. I don’t see it happening once you honestly answer the questions of DDform 2807 questions 26 & 27 at the very least.
Your biggest hurdle is you are drawing 90% disabled; how has that changed? How have your conditions changed….not what you think you can do, but what has changed since a medical diagnosis was made; not your self pride. In other words, how have you healed to the point of being fit for duty when you were discharged for not being fit for duty.