All major hypervisors support ova templates
I was talking about providers.
Hypevisors may support a million things. That doesn't mean that all features are exposed to end users by cloud providers.
Cloud providers have very restrictive policies as to what you can run and how you can install new OSes. Most give you a specific "supported" list of OSes and that's it.
Many support custom ISOs. But I've yet to see one that supports (in a self service manner - after all we are talking about "Cloud") installing a raw .img or an .ova.
These installation options are "OK" when you own the hardware. But are almost useless when you want to use CHR as an enduser/customer of a cloud provider.