Will a National Guard soldier be able to use Military Paid Parental Leave with terminal leave if they have a child while on deployment?

You can not.
This is in AR 600–8–10 Leaves and Passes
The MPLP applies to active service Soldiers, Reserve Component Soldiers performing active Guard and Reserve duty or full-time National Guard duty for a period in excess of 12 months, and Reserve Component Soldiers performing duty under a call or order to active service in excess of 12 months. These Soldiers are referred to as “covered Soldiers.” A period of active service of a Reserve Component Soldier may not be extended to permit the qualifying birth event for maternity convalescent leave when a competent medical authority (supported by the MTF commander, the USARC Surgeon, or the Regional Support Command Surgeon) determines it is medically necessary.
May be taken consecutively with maternity convalescent leave and/or approved ordinary leave. However, primary caregiver leave may not be taken consecutively with chargeable terminal leave and/or administrative absence for transition.

A bit out of my experience, but I would recommend a chat with your local JAG whether that be an OSJA (Office of the Staff Judge Advocate), LAO (Legal Assistance Office), or BLO (Brigade Legal Office) and then of course a trip to Finance to get more information on this question.