Are people allowed to collect unemployment when they're fired? especially fired for drinking on the job?
Not in most places. Of course he'll lie, and an overwhelmed UE office may not check with the employer, but ultimately some costs of claims come back to the employer and they are supposed to be notified and given an opportunity to say whether or not it was for cause...which leads to a certain amount of lying on the employer end of it, and so the UE offices won't necessarily take the employer's 'For cause' response at face value.
Generally bad employees who get fired for cause don't
exactly claim it wasn't for cause, they'll say it was written up that way but that the 'cause' wasn't true, and the whole thing was really just a subterfuge to fire them for some improper reason, like disability or race/gender/ethnic/religious discrimination.
They may or may not give him benefits while they figure out which one they want to believe, depends on the location. In normal times the UE offices range from ruthlessly hardhearted to giving the employee every benefit of the doubt, but with so many people drawing benefits for so long now, most of them are more tightfisted than usual.
I'm sure the Twixie Pixie will come up with a tale of rationalization that will rival the Pittmeister or the unlamented MythSage in its fanciful embroidery of a few threads of truth in a grand tapestry of total BS.