Resin
As of this writing (July 31, 2007), Resin isn't officially supported, although some attempts have been made by Terracotta an others to get Resin and Terracotta to work.
Here's a forums thread on the topic:
http://forums.terracotta.org/forums/posts/list/244.page
Geert Bevin experimented in early July with Drupal running on Caucho's Quercus, a Java implementation of PHP. This led to some experimentation with Terracotta underneath Resin.
See the discussion of Drupal for more info on Terracotta and Resin.
Lab Project
Note : there is now a labs project underway at labs:Resin Support
Note that the experimentation that Geert did was using the Resin 3.1.x development branch. For production, the 3.0.x branch is currently recommended and I think that TC support for that version should be considered too. Resin 3.1.x uses a watchdog (java) process to manage Resin instances. This was not the case with 3.0.x.