Matthew,
with the currently released xowiki version, one can mount an xowiki instance under each community and use e.g. a static portlet to link to it. we use this approach currently for our help desk.
It is straightforward to turn xowiki into an dotlrn applet, but this has on its own only little advantage. Michael Totschnig of our learn@wu team started this week into looking, how arbirary xowiki pages can be used like static portlets. Ideally, one should be able to choose on dotlrn/configure page from the available xowiki instances/pages to include these on portal pages. Additionally, an overview xowiki portlet to list the xowikis of all communities, where one is member of might make sense.
-gustaf neumann