I don't really know, they definatley did not make a cameo appearance
It says in the Jerry Nelson page at Muppet Wiki.
i just literally walked in from seeing it ...im in tears...tears of joy, sorry happiness you name it i loved this Movie...and i knew that i would and i have, had share hope that all you naysayers will watch it and be amazed..The Muppets never left and didn't lose their magic and this movie proves it..DO NOT WAIT GO SEE IT
Jerry was the voice over during the Muppet show telethon.....
NOW i must say this Jason Segel Amy Adams and Chris Cooper DO NOT take any face time away from the Muppets...this is a Muppet filled movie and practically every scene has them...there where countless pictures and references to Jim Henson from original Kermit Clips to you name it, and so many references to the older movies us older fans will love,i want to say so much more but i cant because i dont want to spoil anything....all i will say is it ended and i wanted more...not because it felt short but because i want it...GO SEE IT...i will definitely be back in the theaters to see it, and not just to support it but to enjoy it.