I'd like to create a dexterity type that has a user Field.
I have used Products.UserField before but I'd like the new type to be a dexterity type.
Is there any equivalent for Products.UserField?
No, I don't believe there is. Variety of supporting widgets is probably the single area in which Archetypes is still stronger than Dexterity.
It would probably not be difficult for a programmer familiar with z3c.forms to port the functionality. But, somebody will need to want it enough to make it happen — either by developing it themselves or by hiring a developer / offering a bounty.