Hey mate,
If your fan is rated up to 7.2v then plugging into your 2s Lipos shouldnt be too much of a problem. They chuck out 7.4v (8.4v at absolute max when initially run)
Im not 100% sure, but think that your RX will be throwing out about 5v due to the BEC in your SP ESC.
If it were me, I mit be tempted to make sure there is an adequately rated capacitor between the batt and fan to smooth out the power delivery.
Im no electronics professional so insert disclaimer here
