Those pygmy date palms are really sturdy, I think they will be fine. I have one that has been in the same pot for 6 years, it's even off in a corner behind the pool and doesn't get much sun anymore. It's fine and putting out new fronds all the time. It also has roots that are above the ground, I don't think it matters. I'd use a really sandy, well draining mix around it and put it in the ground but a little elevated as said above.
