Yes. They're fine, assuming it's had some organic matter added to ensure drainage is adequate. I've never had anything but heavy clay. They're perfectly happy in it, and I've had them in every garden.
It's a place where beautiful isn't enough of a word....
I agree with @Fairygirl - altho some of the newer varieties may be a tad picky, just look around - any bit of waste ground, cracks in walls and there is usually a Buddleja growing.
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I've never had anything but heavy clay. They're perfectly happy in it, and I've had them in every garden.