If a Guardsman recieves VA compensation from a tour of duty but then recieves an OTH then would they lose their benefits?

Simple answer is yes.

If you served a full period in the military, received good paper such as an honorable discharge, and immediately re-enlisted for a new period of service that ended with bad paper. You will be eligible for disability compensation benefits only for the period of service that ended with an honorable or under honorable conditions discharge. If you were injured during the enlistment period that ended with bad paper, you will not will be eligible for disability compensation.

You will remain eligible for VA benefits such as health care and education based on your "good" period of service, even if your bad paper was as serious as a dishonorable or bad conduct discharge. One other important point to know with regard to the character of discharge is that VA can grant benefits for an injury or disability which occurred during a period of honorable service even if the veteran later has a period of dishonorable service. In fact pending a VA determination a former service member may still be eligible for benefits even with A "Bad Paper" discharge (See the VA Website for further details. Link below). "Generally, in order to receive VA benefits and services, the Veteran’s character of discharge or service must be under other than dishonorable conditions (e.g., honorable, under honorable conditions, general). However, individuals receiving undesirable, bad conduct, and other types of dishonorable discharges may qualify for VA benefits depending on a determination made by VA."

https://www.benefits.va.gov/benefits/character_of_discharge.asp

If you are honorably discharged and receive benefits for a military related incident, if it's permanent I don't know of another reason for them to stop your award.