Can I install floor outlets on a sub floor then cover them over with portions of the hard wood?

First off check with your local building inspection dept to see if floor outlets are even allowed in your area, If this is approved by them then yes you can install the boxes lower however I would suggest using boxes and face plates for outdoor use to keep dirt out of the outlet.

Check with your buildiing codes to see if this is allowed and only have this done by a professional. Sounds easy on paper, but to have this done properly and look great is another thing. Think hard about placement and you will have to have the placement where it can be done which is not always where you might want the outlets.

I would first install them and not screw them into the subfloor. Then install the floor around them and put on a cover.

You can install floor outlets, but they must be waterproof. You can find these at any electrical supply.