My experience w/ hydrangea is that they need/want shade. That is just MY experience, however.

If hydrangeas have at least 4-6 hours of sun a day, they will be more colorful. I am not sure how they will do against a hot house though, unless they have shade in the afternoon. I have had them on the south side of the house, but shaded in the late afternoon, and had them on the NW side, where they got no morning sun, but lots of afternoon sun. They did great in both cases.

I would suggest you buy one of the little ones, plant it, and see what happens in the next year.