That would be pretty pointless, as DreamHost uses freenode to host their unofficial irc channel
Providing customers support via IRC is also an extremely poor method of support. The current email system and call-back features are perfect for the scope of what DreamHost provides.
Also before I continue, please understand that this is primarily a customer-to-customer forums and while DH staff do stop by once in a while, nearly all of the answers you'll receive are from customers like myself who are only speaking from experience. That said, I believe I can answer at least one of your other questions:
While I don't know about installing OpenLDAP, the possibility to install PHP-LDAP is definitely an option, as custom PHP installs are permitted and documented quite well in the DreamHost Wiki. mod_auth_ldap on the other hand, being an apache module, cannot be installed by your user and would have to be supported by DreamHost. I'm personally not aware of that module being enabled in apache, but I would imagine if PHP-LDAP works then it may indeed be enabled. pam-ldap works well on DH also.
To installing G-Forge - I have no knowledge of that software, so I'd say if you aren't aware of the possibility of installing it as a normal user, then I'd be looking elsewhere for another VPS or dedicated server, as such a shared environment does not typically offer such flexibility.
Nine times out of ten, DreamHost won't install such packages for you either, as it could potentially disrupt the stability of the server you're on (not that I believe it would, but that is the general idea).
If you're willing to try DreamHost host anyways - you could always go with using a promo code, which would initially make the cost of hosting here pretty low (I paid $23 for my first year of hosting) and thus, if you can afford it, it might be worth checking into as far as installing G-Forge goes. if anything you'll have a decent, remote host to store data
Hopefully I've answered most of your questions.. let me know if you need more specifics and I'll try to dig them up.
Chips N Cheese - Custom PHP installs and the like!