Derp.
Just fixed it, apparently you need to add the params to the hook even if you aren't going to use them:
PHP Code:
public void OnPluginStart
{
Handle gameFile = LoadGameConfigFile("tf2.setwinningteam");
int offset = GameConfGetOffset(gameFile, "SetWinningTeam");
g_hSetWinningTeam = DHookCreate(offset, HookType_GameRules, ReturnType_Void, ThisPointer_Ignore, Hook_SetWinningTeam);
DHookAddParam(g_hSetWinningTeam, HookParamType_Int);
DHookAddParam(g_hSetWinningTeam, HookParamType_Int);
DHookAddParam(g_hSetWinningTeam, HookParamType_Bool);
DHookAddParam(g_hSetWinningTeam, HookParamType_Bool);
DHookAddParam(g_hSetWinningTeam, HookParamType_Bool);
DHookAddParam(g_hSetWinningTeam, HookParamType_Bool);
delete gameFile;
}