There's no XO / Executive Officer character in the cast list, and I've searched the character's lines but nothing much comes up except for a Cinema Fanatics article that points to Tom Berenger. It does look like him, but Berenger is the marine recruiter at the start of the movie per the cast list. Is it him playing the XO as well later in the movie, or someone else?
If I had to put money on it I'd say you're right, though can't find confirmation. Had looked up that actor previously and didn't look like a match so ruled him out, but now I see other pics of him that do resemble the character, and the Marine Major he's listed as does appear consistent with being an XO.