laminated was used on This Old House on sunday night - it looked like it had plywood backing rather than HDF, but I don't know whether this is relevant. I think real wood is OK, but I reckon you'd get more movement.
Not really underfloor heating but I have some long pipe runs under my solid maple floor (on top of 1/2" pine) and it does move noticeably more over the pipes than elsewhere. However, there's next to no heat coming through -- wood is a good insulator so why would you use underfloor heating under wood?
We have maple Kahrs Linea (wood construction) flooring down in one room of our extension which has warm water UFH. It seems to be fine as a conductor and if there is much movement then I haven't noticed.
I also have Karhs Linea on top of floorboards. There is a run of about 6 feet from the hotwater tank to the door that contains two hot water pipes that are very close to the underside of the floorboards. These get so warm you can actually feel them when walking on the laminate floor. In just over a year I have not noticed any movement at all.
There's is some good info on the Karhs website search for under floor heating
That's really reassuring, guys. Also a bonus to have two recommendations for the same flooring.
I laid an oak floor in the upstairs landing of our house and in one area the oak board lies almost on top of two central heating pipes (unlagged...there just wasn't the space....centuries old oak beams aren't always where you want them ). This board has shrunk much more noticeably compared to the others (which is what I'd expect) but I just have to live with it.
Edit update: If thick hardwood flooring is a good insulator (but assuming that the insulation of what the flooring is laid on is better) then where does all the heat go? Surely it's going to come out of the floor eventually?