We have hourly employees (working on special projects) and we have salaried non-exempt employees (Admin Assts). We pay semi-monthly. Currently our salaried non-exempts are paid OT for anything over 8 hours in a day. We just added our first hourly who is supposed to be working part time, but has been putting in alot of extra hours since they are working on a lot of extra projects. Could we pay the hourly person for any OT over 40 hours in a week while continuing to pay the non-exempt salaried employees OT for anything over 8 in day?

You would be breaking no laws by doing that, so, yes, you could do that.

Since you already have two different classes of employees (salaried non-exempt vs hourly), I see no problem (other than some grumbling on the part of the hourly person).