It'll work fine for baffles since the connection doesn't need to be waterproof or permenant. Just use silicone to glue the baffles in place.
Silicone is not rated to make a permanent bond between acrylic and glass. In fact, there is no such glue/caulk that will do that.
For the purpose of baffles in the sump it will work fine.
Make sure you get the caulk that is for doors/windows not the kind that is for kitchen/bath. The kitchen/bath kind has a mildew inhibitor in it that is not good for aquariums.
I think the thread is in this forum titled baffles. Who ever did it was showing how they glued spacers to the side of the tank to help support the bafles. GREAT IDEA as the baffles on my 75 gal sump buckled and let go under the pressure and flow that was in the tank.