Had better luck after taking the following steps:
- In 
dotlrn-create.sql, move @dotlrn-communities-package-create.sql up several lines so that it comes right after @dotlrn-communities-create.sql
 - The previous almost works by itself.  One glitch is that the 
dotlrn_community package still relies on a view that doesn't get defined until later.  I did this
SQL> alter package dotlrn_community compile;
Package altered.
which I think solved the problem.  These dependencies could be more clearly ironed out but I'll leave that as an excercise for the student.
 
I have a lot more functionality to look at now.
Anyone else trying this: you need to get a working ACS installed before installing the dotLRN packages.  For error recovery, you can save yourself some hassle by creating an export dmp file after all the needed non-dotLRN packages are installed (caveat: due to some Oracle voodoo I never quite understood, imp'ing ACS4 views tends to be messy, though easily fixed by re-defining the failed views).  Finally, note from the dotLRN instructions that you have to restart the server twice, once immediately after the dotLRN packages have been installed, and a second time immediately after mounting dotLRN into the site map.   Kinda brings back memories of Win98, don't it ;).