RTB is automatically executed before any other add-ons. You should just use something like this:
if($RTB::RTBR_ServerControl_Hook)
RTB_RegisterPref("Enabled", "NoJets", "Pref::Jets::Enabled", "bool", "Server_NoJet", 1, 0, 0);
However, the reason your code didn't work was because you're not supposed to list the $ in the third argument.