It really depends on the terrain and snow conditions. I've gone cat skiing a few times in BC an it's been wonderful powder and mostly treed terrain of varying steepness. On most runs, there are still some options where the guides can tell you "steeper over there, more mellow over here", that kind of thing. And if you don't mind sitting out a run or two, that's always an option if they are going to do something especially challenging (in terms of terrain or snow). I know the one year as we were skiing back down to the base, we did one run that was south facing and they expected the snow to be extra heavy and maybe breakable crust and I passed on that. My husband skied that run and said I probably made the right call.
Now that said, if you're not comfortable in powder, I'd certainly work on that first. I'm definitely not the aggressive skier that I used to be, but I can still ski powder comfortably and work my way around/through obstacles in a reasonable amount of time. Meaning - the group I skied with had some guys jumping the small cliff bands, and I'd pick my way through chutes or go around, but I'd still make it down to the bottom of the run before/right as the cat got there, so it didn't matter and therefore wasn't a race. That said, if you just aren't comfortable skiing powder or are getting stuck repeatedly or are losing skis or taking a really long time on runs... your group would not be happy.
You don't have to be totally matched in ability to the group your skiing with, but you do have to be able to ski the type of terrain you will be skiing in a reasonable range of conditions (I'm thinking if it's really bad - ice crust or something, I'd just bail or they'd cancel the whole thing). Even if you're not quite beating the cat there, it's not a big deal because it takes them a while to load up. But if you would really struggle just to make it down each run, it's not likely to be very fun and you would probably be adding stress of not holding people up to the mix. My husband and I did a guided ski tour of the Aguille d'Midi in Chamonix and there were two Brits in our group that got up top with us, put their skis on in the powder and were absolutely stuck because they didn't know how to ski powder and had never tried (and it was a meter deep that day!). Yeesh. The guide sent for a backup guide to get them back up to the lift because they'd have taken days to get down the mountain. So DO have an idea of what you're getting into.
Personally - I'd check what the cancellation options are, and assuming they're not horrible, really work on your powder skiing skills ahead of the trip and make the final call as it gets closer.
