Personally I do an arm day in between my more serious workouts, instead of a full “rest day”. It gives me motivation to go into the gym, warmup, stretch, get my body healing, but without doing anything that’s very hard to recover from. So yeah, I like that idea.
Upper back is too important to be just done as “extra” though. You should be hitting upper back heavy and with a lot of volume on your upper body days. but if you’re already doing that, throwing in some pullups on arm days or as part of your WOD probably won;t hurt. Just listen to your body - if you feel like you need to skip the gym, do so on these less important workouts. don’t get married to “arm day” at the expense of your important workouts.
Also, tons of WOD’s can be done with just your bodyweight. Not mainsite stuff, but if you take pretty much any 3-5 bodyweight movements and do a 10 minute AMRAP or do 5 rounds as fast as possible, you will be toasted. examples:
50 squats
40 situps
30 pushups
20 pullups
5 rounds as fast as possible
100 pullups, 100 pushups, 100 situps 100 squats as fast as possible
5 pullups, 10 pushups, 15 squats, as many rounds as possible in 20 minutes.
OR you can just make your own. just use pushups, pullups, situps, squats, hanging leg raises, lunges, box or tuck jumps, planks, jump ropes, running, handstand pushups, broad jumps, etc etc. try and pick a round/rep/time scheme that is 10 minutes or less, and work your ass off. if you did that twice a week, your conditioning and work capacity would probably skyrocket, and as long as you keep the workouts pretty short it probably wouldn’t hurt your strength much.