There is no such thing.
The uart will affect p3.1 only if you use the uart to transmit data. If you don't use the uart, the pin is free for other things. No special action needed.
You can always read or write p3.0, even if you have the uart trying to receive stuff. Of course, you will seriously confuse the uart, so you should not touch it if you are using the uart receiver. If you don't use the uart receiver, you can do with it what you want.
I strongly suggest you read the 'bible', it explains the port pins in great detail. It will clear your doubts.
by the way: it is problem, not problume (although it's a beautiful word :-)