OLSR and Captive Portal on the same interface
I finally figured this one out. It makes sense if you think about it, but I thought I'd post here just to save somebody a little time down the road.
If you enable OLSR and Captive Portal on the same interface of a system, you HAVE to put "Allow IP Address" entries in the captive portal config for "From" every IP that you wish for this system to communicate routes with. If you don't, OLSR becomes single-ended (announce only), and the system that runs captive portal will not see any other neighbors or find their routes.
Hopefully this will save someone some headaches.