Reading ZEVO forums at greenbytes.com I ran into a nifty way to solve most of ZFS-over-AFP-sharing problems. To recap: I have a few zfs systems defined on my server pool. When I enable file sharing, only some of those systems show up as volumes on the network. There seems to be no clear indicator of why some systems do show up as volumes so users can connect to them and others do not. Form reading comments around the web it looks like Apple is now hardcoding some HFS file system properties into the software, which delegates alternative files systems to the role of second-class citizens and breaks functionality (including AFP sharing) for them. Bad Apple.
The solution is to trick the AFP server into believing that every file system it sees is HFS: a small library I installed on the server and now all volumes show up in AFP network browser on the client machine.