I think this is a good reference:
http://www.howtoforge.com/how-to-cre...or-ispconfig-3
From what I've been told, the ISPConfig Remote API can use any and all functions that ISPConfig uses. For instance if you can set DNS Slave Zone in ISPConfig Control Panel than you can use this feature also in Remote API. (like I said...from what I've been told) =)