I am right now using nginx 0.8.33 (soon to bump up to 0.8.34) and HAProxy 1.4.2 in production and things work very well for me.
-Nick
Maybe it's worth a try for you to get along with nginx as stunnel replacement ? Its performance is quit good and the config can be held very short, too for only accepting ssl traffic and directing it to haproxy. kind regards, Malte