Do validations still fire in ASP.NET even if the controls are hidden?

If you set Visible to false, validation for that control will not fire. From ASP.Net Validation in Depth:

Why not just use Visible=false to have an invisible validator? In ASP.NET the Visible property of a control has a very strong meaning: a control with Visible=false will not be processed at all for pre-rendering or rendering. As a result of this stronger meaning, Visible=false for a validator means that not only does not it not display anything, it is does not function either. It is not evaluated, does not affect page validity, and does not put errors in the summary.

If you want a control to validate but have it hidden on the page, use CSS to set display to none.