This is antiquated programming. Seam and frameworks on which Seam is dependent, use a different approach to embedded scriptlet.
If you don't want to change your programming style, and embrace the Seam-JSF-Wichet-GWT programming style, you should stay on a pure JSP environment.
Anyway, everything you can do with scriptlets is doable in Seam. Usually in a much more maintainable way.
With xhtml, you use EL (expression language) instead of scriptlets.