Generally, yes.
Supercell’s Terms of Service don’t call out VPNs by name, but they do say you can’t use cheats, hacks, mods, or any unauthorized third-party software that modifies or interferes with the game, and you can’t do anything that disrupts the service (including denial-of-service attacks). So, using a VPN for privacy or safer Wi-Fi is okay, but using anything that messes with gameplay or breaks their rules is where you get into trouble.