Are there any good technical forums where jailbreak app authors hang out?
A number of developers are on IRC on Saurik's IRC network: irc.saurik.com (port 6697 for SSL). Channels include #cycript, #cydia, #iPhone, #iphonedev, and #theos (for tweak development).

Also note you will probably get better answers to jailbreak questions at Jailbreak QA. No questionable questions are allowed there. And you will not get a good response if you have questionable repositories in your Cydia configuration. Just how things are.

Most forums I have found regarding iOS hacking usually involve piracy at some level (whether that be getting apps or in-app purchases for free).