Can I work simultaneously for a Mortgagee as a loan officer, and as a real estate agent for another company?

Yes, if the Mortgagee has determined that the employee’s other outside employment, including any self-employment, does not create a prohibited conflict of interest as described below.
Conflict of Interest:
Employees are prohibited from having multiple roles in a single FHA-insured transaction. Employees are prohibited from having multiple sources of compensation, either directly or indirectly, from a single FHA-insured transaction.
For additional information see Handbook 4000.1 I.A.3.c.iv(B)(3)(b)(iv) and (v) at:

All policy information contained in this knowledge base article is based upon the referenced HUD policy document. Any lending or insuring decisions should adhere to the specific information contained in that underlying policy document.

Topic Number: KA-05109