Given the thrust line of an Up & Go high above a glider's vertical CG location, a nose-down pitching moment will be created, stronger than what a conventionally-mounted motor would generate.

Will increasing the downthrust angle effectively increase the angle of attack, in order to compensate for the pitching moment?

No, you will have to compensate with up elevator, either manually or through a mixer.
Also see thread : "Giant sailplanes" in this forum, towards the end of the thread.

Michael

Hi,

we had the best results with the thrustaxis pointing at the elevator nose. You will always have to pull a little bit while power flight.

MfG,
Armin