Very neat servo mount! For beetles, 3D printed wheels can certainly work. Printed with the more common materials like PLA or ABS they'll support your weight, and take most things that aren't hits from spinners (though most wheels won't survive those). For hubs you'd want some stronger materials, either something strong like Nylon or even steel. You could also implement a square nut into your design so you have something metal to hold a grub screw in place on the motor. Alex Mordue did this for Saw Loser, his build diary is on github.

Another material could be TPU, which is far more flexible. Ben Hay from Team Panic uses it for his beetle AnnieRUOK, check out his YouTube channel if you want to know more.