You got luck with the Art 15 in the restricted file. That is not common. But it is possible...and if you have it...well, consider yourself lucky.
The restricted file is what the name implies. It is generally NOT available to promotion boards...heck, it would not do much good to fight to get records in there if it were available to promotion boards. It is also not available some other selection boards but can be reviewed prior to command selection. It is also available to DONCAF (the folks who grant security clearances)
I say generally since there are exceptions. Under DA Memo 600-2 it can be requested...here is what the memo provides
b. Access to the restricted file.
(1) Restricted file access is governed by AR 600–8–104.
(2) The board president may request that the board review information contained in the restricted file of
an officer under consideration. The board president will state the specific reasons for submitting the request. The convening authority
or his designee will consider each request on a case-by-case basis. Only information directly related to the request may be provided to the board. If the request is approved, the OMPF custodian will place a copy of the approved request in the officer’s restricted file
So it is possible for them to access...but it is not common and would only be available if SecArmy approves.
As for the BOI - if you have it in the restricted file? I doubt they are going to press a BOI...that would not make any sense. If they wanted to kick you out, they would not have put this in your restricted file.
Now...for removal? If it is in your restricted file? You can file a request to "correct" the record, to remove it as inaccurate.
But as I mention, I think you will have a tough time with this...again, you were not found innocent, you were found criminally not guilty. Still, if you want to press this, I would do so with a request to the army board of records correction...you want to demonstrate to them that the record is in error...if you can do so, the board can erase the record