Yes, you can (if implemented, of course: a few kinds of calculations are not available with USPP, a few more are not for PAW). A small restrictions exists in cp.x, expecting atoms with USPP listed before those with NCPP, which in turn are expected before local PP's (if any). A further restriction, that can be overridden, is that all PP's should be generated with the same XC. Otherwise, you can mix and match. Note that it is the hardest atom that determines the cutoff.
First, a general rule: when you ask for a pseudopotential, you should always specify which kind of PP you need (NCPP, USPP PAW, full- or scalar-relativistic, for which XC functional, and, for many elements, with how many electrons in valence). If you do not find anything suitable in the pseudopotential page of the web site, or in the links thereof, we have bad news for you: you have to produce it by yourself. See 4.4 for more.
Please consider first if DFT is suitable for your system! In many cases, it isn't (at least ``plain'' DFT: GGA and the like). If you are still convinced that it is, see above.
What is available (no warranty) is in directory upftools/. You are most welcome to contribute a new converter.