Can anyone say if this is just a hothouse rose, or can it be grown successfully in the garden?

I'm sure it can be grown in a garden, but perhaps not in your garden without extra protection. It's a Harkness shrub and they typically are hardy only to zone 6.

Thanks, Zuzu.

I'll keep it in mind as a "maybe". (If I can even find it.)

Ah, I see that Pickering currently lists it, but their image looks a lot like Polka (which I have already), so I guess I'll pass on an extra protection rose and just admire it from afar.