This may help answer your question...

Here is a link that might be useful: Wood over radiant heat

Check out www.wideplankflooring.com They provide good info. We just installed radiant heat under pine boards ranging from 4 - 12 inches wide. All the info on the web advises against doing so, however we talked with people who have done it with no troubles. We are keeping our water temp. around 100 degrees. I think some of the horror stories probably had very hot water flowing through, like 180 degrees. The newer radiant heat systems run cooler water. The floors have been installed for 2 months now, the heat feels great and I haven't seen any signs of cupping, etc.

Sure you can. The best products are stuff like Warmboard. It allows you to put a subfloor down and then put any wood you would like right over the radiant subflooring.

Here is a link that might be useful: Warmboard

My in-laws have radiant under wood. It's so nice in their freezing winters. They have a basement, which made it much easier to install the radiant system than it would be otherwise.

I have hydronic radiant under hardwood in about 95% of my house. The entry, kid's bath, and laundry are tiled.

Works better than fine.