That's funny, cos the rules linked to in this thread ( Desmo Due Racing Rules 2005) say both are allowed....
http://217.199.188.40/xmb/viewthread.php?tid=13180 Page 2 in the Chassis section.
• Wets are allowed. (Safety issue)
• Tyre warmers are allowed.
[Edited on 16-4-2005 by Mr_S]