PaaS (platform as a service) cloud providers generally limit you to a fixed technology stack. However, OpenShift and Heroku allow third-party extensions, which can be used to support Haskell.
The cartridge comes in several flavours, with just the network package (GHC 7.8.2) or a pre-installed framework (GHC 7.6.3 *):
* GHC 7.8 requires dynamic libraries for Template Haskell and Quasiquoting. OpenShift gears default to a 1Gb quota, which is insufficient for a full web framework with two copies (dynamic and static) of every library.
Frameworks that don't have their own quickstart template use the network template (also included in every cartridge). I'll be happy to include any contributed framework-specific templates - please open an issue with a link to your Github repo.