Currently using Captivate on NMCI workstation - Neospeech is not an approved application. What other TTS software is compatible with Captivate?

I don't really know of an alternative, you should check with your IT department to understand their 'governance' policy and ask for a copy of the procedure document showing how you can get applications approved for distribution, or (in this case) a single exception installed for course development.

One limited, and expensive, alternative would be to hire a vendor to receive Cp8 files with TTS & Caption text identified; and have them return updated Cp8 files with digital audio embedded.

I imagine, it the restrictive *IT centralized* organization you describe, you'll have as much difficulty adding a vendor to the approved vendor list as you will with getting an application added to the approved application list.