My experience has been that the collar won't cause a problem in situations like yours, so you should be OK. If your crank's not designed to fully bottom out, it should end up with an air gap between the collar and the crank. So no harm, no foul.
The bottom brackets have seals or at least dust shields over the bearings, depending on the model. I've seen low-end ones where the bearings were visible after losing their dust shields, but that's not normal. Glad to hear you're getting the UN-54, they're worth it in the long run.