Combo works IF you're only doing 2 maybe 3 things from each.. not going to make as good progress with the other.
It's like combining strength + endurance. Your results will be less than each but you can make fairly decent progress in both.
I'd probably say cycling them is much better if you did 6-8 weeks wtih one then the other plus continuous skill work from gymnastics.
5/3/1 is a stand alone program.... not sure itssuch a good idea to try combine with another whole half a program if that.