Can I file an IG complaint against an E-8?

Obviously you can. You do not provide enough information to help us help you decide if you should.
As others have said, if the SNCO in question is in your CoC, I would assume you have exhausted all means of addressing whatever is happening up to your CO. If not, you better make damn sure the first time your command team hears about this it is from you, not someone calling from the IG office.
Always settle issues at the lowest level possible. Escalate only if necessary. If this is simply a personality clash, you will lose. If it is something more serious, do what you have to do.

From the IG Desk: AR 20-1 provides that no service member may be prevented from access to an Inspector General. Make an appointment - you can't simply walk off the job. Concerns may also be communicated anonymously in writing or by phone...an IG takes ALL input seriously. Ensure your concern rises to the level of an "IG Issue" and is not just the perception of a pet peeve or imagined slight. Use your Chain of Command (CoC) prior to visiting an IG - that's the first question I always ask and may refer a service member back to their CoC if they haven't attempted that route initially. If the concern is with a superior, attempt to work it out at that level. If unsuccessful, see the next higher superior for resolution, keeping in mind all service members have access to their Commanding Officer. Certain concerns may be better addressed through the offices of Chaplain or Equal Opportunity and an IG may recommend that route. Resolution of a service member's concern, if accepted, will be investigated and the results discretely communicated to the Commander for action (those results may not be communicated back to the service member). Be aware that illegal or potentially dangerous activity reported to an IG will be immediately forwarded to appropriate authorities for action.

Just make sure it's not 'my 1SG doesn't like me'.
1SGs don't like anybody.
;)

Sure, but you’d better have your stuff together and have exhausted all means of resolution with your COC to save yourself some embarrassment. I once had a soldier that had come to the Army after serving in the Navy. Long story short, she wouldn’t train in MOPP gear and complained all the time. After several informal and formal counselings, she filed an IG complaint for sexual harassment on me (I was her 1SG). There was an investigation, my COC backed me up, and of course I was exonerated. She was soon transferred out, as she had alienated just about every EM and NCO in the unit.

Solve problems at the lowest level, directly approach and have a discussion. If too intimidated, grab an unbiased third party to approach with you, send an email etc. Filing a complaint should be the last step.

I once made a complaint against the Finance Office in Benning. I was an SFC assigned to a TRADOC unit and got a No Pay Due at the end of month.
Not having any known encumberances or anything I could think of I called Finance and was told Oh, your pay was given to an OCS candidate for a debt????
I was livid, not only didn't I know anyone in OCS, the Finance clerk on the phone told me I needed to address the issue with the OCS Candidate and if the debt wasn't valid deal with him and his OCS COC. NOPE, not going to happen.
Got on the phone with IG, called OCS Commanders office and double-tiimed down to the Finance Commanders office. Was a hell of a fight but I got paid by the end of the day! Turned out the OCS CXandidate owed a bunch of money on a car and a judgement was made against his pay, the Finance folks messed up and charged it to my account then tried covering it up by trying to get me to go after the OCS kid rather than their mistake.
So yes, you can pretty much file a complaint against anyone.

Yes, you are free to complain against anyone to anyone, and good leaders will make the time to listen to your concerns. Inspectors General would take your case if the root cause of your issue would have potential impact to the overall efficiency and effectiveness of the command. It's also possible that the IG would take your case as part of IG's function for performing assistance to individuals, but as part of their fact-finding process, would conduct interviews throughout your chain of command to see if you have done your due diligence to solve the issue at your level.

Do not for get to use your chain of command .

Yes you can try. If you have evidence of fraud, waste, or abuse by a military member you can contact the IG. If you have evidence of criminal activity go to law enforcement. Either way have your stuff together. Bring relevant documentation. Be prepared to answer lots of questions. It will be a learning experience.

Can you? Yes. Should you? Make sure you have your ducks in a row before you proceed. Slippery slope!