All the ground connections are common on the board in the controller, so yes, this works fine. I've done much the same on my current folding bike, just to reduce the number of wires coming out of the controller. The only thing to watch is the +5V wires, as the feed for the throttle usually has a series diode (it does on all of the 6 FET controllers I have, for example, and on the 18 FET one I have). This means that the throttle "+5 V" isn't 5 V at all, but around 4.4 V to 4.6 V or so. The Hall +5 V is a true 5 V, fed directly from the +5 V rail. Best check your controller to see if yours has the series diode in the throttle connection. The work around is to use the Hall +5 V to run both the throttle and the Halls, and if you get the over-voltage cut out throttle problem at full throttle, then add a series diode in the wiring loom to the throttle +5 V feed, leaving the Halls with a true +5 V but dropping the voltage by half a volt or so for the throttle.
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