It depends. What functions do you want these sims to be fulfilling in your world? When they come into your world, they do have to be in proper households once unpacked the Porter way so they will be residents at first until you step and do something else with them.
--Homeless Role Sims -- can do; evict them from their houses so they are no longer residents but first assign them the roles you wanted with Register.
--Homeless Service Sims -- tricky. You can make the sims you have Portered into Service Sims with MC Cheats' Sim > Advanced > Set Service command, but there is no guarantee that they will be used as such or stay in the service pool.
-- Homeless Co-Workers or just hanging out in your world fulfilling no function -- also tricky. I mean, you can do this but chances are they will just wander out of your game on you and more quickly if you use SP to Manage the Homeless and/or Overwatch to Cleanup the Homeless on its overnight runs (I use neither myself).
Homeless sims are volatile and we do not have complete control over them. We can control the sources of the genetics used to spawn them instead using SP with the SP Population module, and we can review that procedure if you want, but that 's not quite the same thing as bringing in an exact sim to be a maid, babysitter, etc., or a generic homeless vagrant, as the game likes to call them.
