No, Sitecore MVC forms are not directly compatible with an ASP.NET site build using Sitecore. There are a couple of reasons for this:
Technology preference: Sitecore itself has transitioned towards using MVC as its primary framework. While ASP.NET Webforms can still be used in conjunction with Sitecore, it's not the recommended approach for new projects.
Architectural differences: Sitecore MVC forms are designed to work within the context of Sitecore's rendering pipeline and data infrastructure. ASP.NET Web Forms has its own way of handling forms and data, which might not integrate seamlessly with Sitecore's functionalities.