Depends on the lounge. UA swipes it, but will enter if your mag strip doesn't swipe (I have the same issue -- seems very common with CO PC cards). UA's backup is to scan your BP, but since my BP has my UA1K number in it, that just makes more work for them, since they have to delete out some of the info before entering the CO info into their lounge entry system.

Some other lounges document the number. Others just write down a tick mark in a CO column and charge CO that way.

The recordkeeping really varies by lounge provider.

But to answer your question, an unscannable card should not be a problem. They're probably used to it with CO cards.