i dont know where you read that you need to use a sense rom in order to activate your phone.

that is completely wrong.

the droid x (when i had it) requires bootstrap recovery, mainly droid x/ or droid 2 bootstrapper to install custom ROMs
however if you go to 2init roms you do not need that bootstrapper, problem is, it needs to be installed first in order to flash the 2init roms.

you can install cm7 or cm9 whenever you want as long as you are rooted, and have droid x/2 bootstrapper installed.

if you need more clarification please do not hesitate to let me know.