The current version of baikal in portage has a hard dep on dev-db/mysql. This should be changed to virtual/mysql so that it can also be used with, eg., dev-db/mariadb. I've tested with mariadb as the backed on my server and all seems to work fine.
Also, it would help to add webapp_pkg_postinst to the pkg_postinst() function. This will allow the user to be informed of how to complete baikal installation using webapp-config. This isn't really related to the original bug, but it's such a minor thing I figured I'd tack it on here rather than opening a new bug. If you'd prefer I open a new bug instead, though, just let me know and I'll be happy to do so.
Thanks, fixed!