Yeah, I HIGHLY doubt they will support non-Garmin transmitters. I'm just saying that the scant info I've seen so far does not rule out the possibility.
If they went to all the trouble to (stupidly!) develop their own transmitter, then they are pretty unlikely (in my estimation) to give their customers a way to use some other company's transmitter instead. One, that would undercut their sales of their own transmitter, which I'm sure they will be trying their best to have recoup their R&D investment in transmitters. And, two, that would make it too easy for someone to compare the two types of transmitters in a real apples-to-apples manner, that might show that the PPS transmitter is better.