This would be Uncle Deadly's first actual appearance in a Muppet movie, wouldn't it.
You know, I'm about 2 minds with this issue.
On the one hand, I'd also love to see the newer characters but at the same time, we haven't seen Rowlf utter more than 3 syllables in a movie since MTM. His last theatrical line was a short "Awwhg!" Was Thog even in a movie before other than the Rainbow Connection reprise at the end of the first one?
There are TOO many Muppet characters to all get screen time, and I'm sure they hammered out how many want to use long ago, and again, I wouldn't count new characters out. Even if they weren't written in the script, some of the Muppet employees (writers, puppeteers) could have twisted some arms.