Can a leg day count as a rest day for my upper body?

You sound like those noobs that just started going to gym and yet no nothing, not even the basics about bodybuilding. No leg day does not count as a rest day for your upper body, because you're still exhausting yourself and using other muscles during some compound exercises such as squats and deadlifts. The reason why you are supposed to be having a rest day is because you are to cease everything, not even work a single muscle in your body, doesn't matter if it's upper or lower body. Your body is meant to break the pattern of being used to working out, since your body hasn't had a break, it is now used to working out and won't be making any gains and you will plateau very soon, or probably already have. That's why you're not supposed to be working out 7 days a week. God you're an amateur. You should work out 5 days a week max. Combine two muscle groups a day when you work out. Separate your days, between rest days and working out days. I do biceps+forearms+abs on monday, tues- chest+ tri, wed- REST, thurs- Shoulders+traps+abs, Fri- REST, sat- back+legs, sun-REST. Oh and every so often amount f weeks, you are supposed to take a whole week off training, or else, again you will plateau, roughly every 7-8 weeks. And you're supposed to change your workouts every 4 weeks.