You don't need to open source it to make it compatible with OJK. All of the stuff I was shown for hooks used is irrelevant with OJK engine. I only see you being the ones complaining instead of making 1 cvar to turn if statements off (That cvar can be the version string of the engine for runtime detection even). Wouldn't even have taken you 5 minutes a year ago. The alternative method would be to take a little more time and use the newer API. But then you are semi in the grey area of using GPL code in general. Note: Fix your shitty ass site so that it doesn't get blocked by NOD32. This will also detect jamp.exe on windows so you might need to get more creative.
char version[MAX_CVAR_VALUE_STRING] = { 0 };
trap->Cvar_VariableStringBuffer("version", version, sizeof(version));
if ( strstr( version, "2003" ) ) {
// do JAMP stuff here
}
else {
// OJK or other non jamp compat engine
}