Hello,
First, glad that PlantUML can help you : was it used for Higgs boson search ? :-)
About C++ comment parsing, I am not sure of what you are looking for, but since C++ comment are the same as Java, PlantUML code in C++ comments should work out of the box.
About hyperlink, you can find some information here : http://plantuml.sourceforge.net/incubation.html
Yes, we are interested in collaboration : many features comes from users idea's and suggestion!
You can either propose what you are expecting here, or send a mail to plantuml@gmail.com
Regards,
Arnaud