Cascade supports forms (i.e. if you manually enter the html tags for a form, Cascade will not corrupt them).
Cascade is using a php implementation of FormMail. The URL of the instance UVic is running is https://web.uvic.ca/fm.php . Technical docs on that are at https://github.com/andrewmriley/phpformmail, and they look very similar to other implementations of FM I've seen.
I've implemented a form on the UNI101 site. It is mechanically working, but will probably need some tweaking (e.g. error handling, layout) based on feedback from BC.