Thanks for the questions. WebUI Test Studio should be able to capture verifications that are added to the Dom for that page as long as the sequence of recorded test steps result in expected values just as a user would interact with the page.
The Rad and Html control translators attempt to make verifications easier for you by giving Quick Tasts in the Elements Window for a particular element. You can also create your own verifications as in this video
. You can also use the new 3D mode in WebUI 2.0 to create verifications as in this video
As far as your other question, I'm not sure what you mean exactly. Are you talking about wrapping either a Rad, Ajax, or Html Control in custom code with a custom tag? Please go into further detail with this question.
All the best,
the Telerik team