Any time you are off work without pay, you need to file for unemployment insurance. If they say you are terminated, they must prove they had a valid misconduct reason to fire you. If they cannot prove you were smoking, and you insist you were not, and have a witness to that effect, it would be hard to stop you from being approved for unemployment insurance.
It doesn't matter whether you and your co worker "go down together to file for benefits." Every unemployment claim is separate, they will not take information from your claim to make a decision on your co worker's claim and vice versa. So it doesn't matter until you get to an unemployment hearing, if you are denied and appeal, or are approved and the company appeals, each of you could testify in the other person's hearing that the two of you were NOT smoking.
As far as firing you or putting you on "indefinite suspension" which is about the same thing, they can do that. Your union steward is saying he cannot help you, or even if he can, it may be several weeks, and in the duration, you need to file for unemployment benefits immediately.