|I know that the two hunt joining are still possible, but i have suggestion about combat joining.|
If your hunt is peace of cake they will run for they lives so your hunt will start when you will catch them (in 60 s, or 45) or they will come to collision with other hunts from the same area within +/- 1 lvl. The higher challenge lvl less time needed to catch them or they will start to fight you back.
If the hunt are challenging (they think you with your troops are history) so they will start a fight straight away and there is no chance (or tiny) to collision with other hunts (it wont spoil your goal for top hunts.
so in the end hunts with low challenge lvl have chance to catch with red hunts.
Still i think it would be low possibility...