Originally Posted by bgriff

Yes.

You will arrive in Terminal B or C and will need to clear US immigration and customs (and, if you have checked bags, reclaim your checked bag, and then recheck it after clearing customs). Depending how long that takes and how long your connection is, there may not be a ton of lounge time.

If you arrive in C, it's probably easiest to reclear security there, and then take the airside (post-security) bus to A. You could also use the United Clubs in Terminal C before leaving C if you wanted, though leave ~20 minutes for the bus (wait + ride).

If you arrive in B, you can take the AirTrain to A, where you'll have to reclear security, and then could use the United Club there. (It's a bit of a walk from the AirTrain station to A, and security lines in A can be long, which is why going through security at C is easier if you arrive there.)