I only have an Ultra, and I don't know if this "limitation" has been fixed in the II, but I am personally disappointed that the Ultra does NOT have a separate output 2 mode. I would almost always use STEREO for Out1 and MONO for OUT2, specifically because I want to be able to use a single RCF some of the time (I don't bring my two units to rehearsals, for example).
The alternatives, in the absence of an Out2 mode, all have nasty side-effects:
1-) Use MONO output for both Out1 and Out2. This sucks if you're lucky enough to have a stereo FOH
2-) Use STEREO output, but plug your single RCF in only one of the two Out2 jacks (either L or R). This sucks because you only get one half of your signal chain. If you have two amps and/or two cabs panned anywhere other than dead-center, you lose that. Also, you lose any ping-pong or stereo delays.
3-) Use STEREO output, and plug both Out2 L and R into an outboard mixer, pan both channels to center, and send the mixer output to your single RCF. This sucks because you need an extra piece of gear (can't my Ultra replace a silly old two channel mixer??!??!?)
Another consideration is phase artifacts. If you collapse both channels (L and R) to mono as in options 1 or 3, above, some effects settings may cause phase cancellations. I personally test all my presets to avoid such artifacts, because I *constantly* run a hybrid STEREO *and* MONO setup (stereo to FOH, mono to a single monitor). It's a tedious piece of work, but absolutely required. With options 1 and 3, or any other method of collapsing stereo to mono, you need to verify all your patches for phasing issues. That would also apply if there was a MONO mode specifically for Out2.