Possible to print a field and be used in another module's submit form?

I'm creating a custom module used for maintaining accounts for an off-site system. The users that use the off-site system are users that use our Drupal installation. I'd like to use one of our user reference fields in this module and submit the referenced values alongside the module's form like any other field.

Is it possible to print a preexisting user reference field in another module's form and submit those values with the form's other values without impacting the settings or data that the field already has?

(I just need a user reference field in my module's form that I can use to reference users and submit with the form's other values.)

Any insight into this would be appreciated.