The S1 is a stand-alone miner. You could run the rockminer together with the USB one though.
You can certainly point all to the same pool.
You can probably run both the USB one and the Rockminer on the same instance of cgminer, however if that gives you problems, you can always run separate instances of cgminer/bfgminer for each of these. At some point I had 6 instances of bfgminer/cgminer running on the same old win7 laptop with a garden variety of miners. Just read the 'readme' files of these mining packages and use the latest ones if your miners are of a recent 'vintage'.
Cheers
Yeah, shouldn't be a problem, should it? As long as the software miner knows how to talk to the miners, it should recognize them. I only have hands-on experience with an array of ASICMiner Block Erupters, so they were all the same hardware miner. But it shouldn't be a problem as long as you point them all to your account in the pool.