Hang gliders are meant to be very difficult to get out of underwater - my instructor used to compete in the birdman competitions and told me it's not to be underestimated. It may be easier (or harder) in a trike.
I will admit to ditching a hang-glider. The worst of it was the embarrassment. Witnesses thought I was done for, but I was treading water under the sail with my head out of the water, trying to undo the carabiner on the hang-strap. I never did manage to undo it, but eventually got a foothold and carried the wing through the surf intact. I then set it down on the beach too early and a wave rode up the sail smashing some battens.
In the water it is always going to be easier to undo a seat belt on your lap than a carabiner at your back. So yes, it would be easier to get out of a trike.