After many days of intense swearing (HAproxy is now referred to as piece of shit in my internal lingo), this is where we are.
pfSense generates the config.xml with proper <ssl>yes</ssl>
pfsense generates the haproxy.cfg with proper server "id 102 ssl verify none"
But even after restarts, haproxy still does not bridge
printf 'show servers state\n' | socat - UNIX-CONNECT:/tmp/haproxy.socket
101 TEST-ldap.mintsecurity.fi_ipvANY 102 login-02.ipa.mintsecurity.fi 10.98.0.25 2 0 1 1 1340 9 3 4 0 0 1 1 - 8443 - 0 0 - - 0
But the culprit is /tmp/haproxy_server_state. Delete that, restart, and then:
101 TEST-ldap.mintsecurity.fi_ipvANY 102 login-02.ipa.mintsecurity.fi 10.98.0.25 2 0 1 1 449 1 0 2 0 0 1 1 - 8443 - 1 0 - - 0
You see, the very important 0 that turned into a 1.
I have NO IDEA if this issue now is persistent, if every modification will require the deletion of the state file.