I think the only "issue" might be the phone number that you have registered the Uber account with if they need to call you as a UK Uber driver is not likely to want to call a US mobile if he she needs to. Perhaps there is a simple way around it. Having said that I have used UBer with it registered to my UK number in the USA with no issues so it should work seamlessly the other way around I assume. If you really wanted to it is easy enough to go into Settings and edit your account and put your UK number in there.