Speaking from a 1 M/E standpoint, I’ve been able to use the ‘Pro’ Panasonic cameras (AG-HMC150PJ / AG-HMC80PJ), as well as a Sony consumer HD camera with no problem. With the Sony, I’ve only used a 1m microHDMI/HDMI cable, with the Panasonics, they’re unstable over 25ft in 1080i.
I’ve been fairly successful with HDMI extenders from Monoprice. They have one for $40 that will do 190ft over Cat6. I did get one DOA, and am about to start the return process, but the other two have worked flawlessly.
I have noticed, in addition, that the Panasonics have three output options: Auto, Fix, 480. The latter is a downconvert, the first two will work with the ATEMs in HD mode. However, the camera can get confused on AUTO if the ATEM doesn’t feel like reporting its true resolution. If you can do any sort of ‘fixed’ output resolution that matches the mode your ATEM is in, it only takes a second or two for the initial sync after connection.