Why would you do that? You aren't using them both to work your lower back(unless you are doing them wrong), so why would you do them on the same day?? Deads are for back. Squats are for legs. They should be separated in my opinion, if you want to get the most out of the two. Doing both on one day as a switch wouldn't be a bad idea, as your body needs a shock every once & awhile, but as a standard way to train it isn't wise. You wouldn't get the most out of both exercises doing that.
Also, if done correctly, then the primary muscles involved in a standard dead, are the entire spinal erector section. From ass to neck that is, and not specificly the lower section as you stated. Deads do hit your lats as well brother. They are a secondary during the lift, but they will get work.
If you wanted to do a deadlift version on leg day, then assuming that you do both quads & hams on the same day, you will get more of a PRIMARY leg workout if you did straight legged-deads as opposed to regular deads on that day. Straight-leg-deads target the hamstring muscles primarily, along with the spinal erector to a lesser degree. If you are thinking of doing deads with squats thinking that you will be working the legs during both lifts, then you are mistaken bro. If done correctly, the legs(both hams & to a higher degree quads) are only stabilzers in a regular deadlift.