If he can handle both, there's no reason not to do both. I just find that I can only give one or the other 100% effort. I mean, geez, I was ready to go home yesterday after deads and I still had the whole rest of my workout to go! No way was I gonna do squats too!
If you pull from the floor, or even better a platform, Deads are very much a leg movement, so in that sense they would replace squats. Their hip-dominant however, so I typically incorporate a less taxing quad-dominant movement on dead day: lunges, single-leg squat, etc.
You still end up doing total body, I'm not suggesting a split. One day would be squats with some other back/hip movement, the next deads with some other quad movement.
Throw in a couple of upper-body pushes and another pull and you're set!
However, don't think that I'm trying to say "I'm right and you're wrong" - cuz I'm not at all. I just trying to display some of the options and versatility FBT can offer.