My understanding of TM751's is that they don't respond to RF.
I have to have the TM751 plugged in right?
Now if I add the CM15A, and take out the TM751, will my camera remote or palmpad remote still work?
No you are a bit confused. The TM751 does not respond to PLC - X10 signals over the powerline. So you could NOT control the outlet in the TM751 with a "Maxi Controller", "Mini Controller" etc , - any wired controller that sent only PLC codes.
The TM751 responds only to RF. It receives X10 RF commands and and couples them on to one phase of the homes powerlines as PLC, so yeah, it has to be plugged in(?).
The Palm Pad and Camera Control (not the Ninja control) will continue to work because the CM15A acts a tranceiver (receives the RF command and transmits it on the powerline as PLC commands) just like the TM751.