Found the problem. I reinstalled SE and removed my ~/.slickedit/13.0.0 directory. Ran vs, and got the license failure window. And I noticed the window indicated it couldn't find the license file in /opt/slickedit.
I installed in /opt/slickedit_13 (paranoia on my part - I always install into /opt/slickedit_## for each version). When I renamed /opt/slickedit_13 to /opt/slickedit, everything worked correctly.
So there is apparently a hard-coded path somewhere in the license code, looking for /opt/slickedit. Interestingly, even when I put the license file in ~/.slickedit/13.0.0, all 3 executables (vs, vs_fileonly, vs_sharedxft) segfaulted.