I should point out that I'm neither a FreeBSD nor an OpenVPN user. Any advice I can offer would be either PF-specific or networking generic.
If you'll post your RELENG version, I will at least be able to figure out which revision of PF is being used. There have been many changes over the years that affect both capabilities and syntax.
http://forums.freebsd.org/showthread.php?t=39295