I've seen in the contracts-upgradeable repository that you still have access to the EnumerableSetUpgradeable.sol.
Does this mean that they place nice together and don't cause storage issues when adding/removing to/from the array when it comes to proxied contracts?
EnumerableSet doesn't have storage, but we still offer an "upgradeable" version so you can be sure that you're using a contract that is safe for upgrades.
Thanks @frangio! 've dived deeper into how arrays are stored in solidity too and so can see how the EnumerableSet pattern is upgrade safe so long as the usual caveats for upgradeable contracts are applied.