A character without enough UMD to use an equippable item can still use that item by temporarily boosting their UMD to equip that item.
With Bard Song, a Palanthir of Knowing, Cha boosts, and various magic rings, even a character with almost no UMD investment can wear gear - even hold weapons - that are class, race and alignment locked, that they would be otherwise unable to wear or equip. They can then safely remove the items and buffs that are boosting their UMD score, but the special gear will remain equipped for as long as they're logged in.
Krosenq recently asked in Discord: is this an exploit? DM Agony confirmed that
yes, this is an exploit. You shouldn't be using gear that you don't have the UMD to use. But noted that EO should probably clarify.
When a character with such gear equipped logs off and back on, the gear they're using that they don't have the UMD to use will automatically unequip - even to the point of stripping the character naked in public. This suggests that it's not intended behaviour that UMD is forever. And if you're holding a sword with an opposite alignment requirement to your own, it might make sense that when your UMD drops back down, you find that sword too odious to hold.
But this is also default NWN behaviour. I'd always put it down to NWN jankiness: it presumably only makes the check at the moment of equipping the item to save resources. It's also super, super common player behaviour. Palanthirs are often used in the moment to equip gear, because you only need to bring out the orb once and then put it away.
According to Agony, per PnP, when using an item long-term, you're making a UMD check every hour. I don't know if there's a way to force an update like that every in-game hour, but that would bring the server back in line with PnP.