Hello Scott,
Looks like the problem is much deeper and there is a very high possibility that either your server is compromised or the hackers have access to a vulnerable script in your server.
They are basically re-creating these users using either vulnerable script or a backdoor in your server after Bulk Delete has deleted them. Also these users are getting directly inserted into the DB and that is the reason they have the user role set as ‘none’.
Even if you delete them directly from the DB, these users would get created again.
You need to solve it in two steps.
1) Find out which backdoor or vulnerability that hackers are using and the fix/block it.
2) Once that is done, delete the spam users from the DB directly.
Also make sure you backup everything. Since the attackers have access to your DB, it may be very easy for them to delete everything that is present in your DB.