Wiring – Help Wiring Ceiling Fan With Dimmer Switch

This deal is sorely in need of some colored electrical tape. Seriously.

There is one /3 cable (black white red) since ground is not counted as a conductor. It is the same cable both in the fan box and the switch box. On this cable:

• Mark both ends of the white wire with black tape, to designate that it is for "always-hot". Use of the white wire for always-hot is mandatory in this case, but also mandatory is the marking I just described. This is the only mandatory marking; the rest a done for sanity's sake.
• You see in the switch box where the white wire joins a black and red wire in a wirenut. They are both short pigtails, also mark the red wire with black tape near each end, which will reduce confusion in that box.
• The red wire exits the cable in the switch box, and hits a wirenut to connect to a red pigtail that goes to a switch. We'll leave that all red.
• The black wire exits the cable in the switch box, and hits a wirenut to connect to a red (!!!) pigtail that goes to a switch. Annoying! So we will:
• get blue tape, and on the /3 cable, mark both ends of the black wire with blue tape. Also mark the red pigtail with blue tape.

Ok, now counting the tape color, black = always hot, blue = switch 1, red = switch 2 and white is neutral. This just got a whole lot easier.

Up in the fan box, black gets nutted to black (which is the white wire remarked black, and NOT the black wire remarked blue).

Three wires remain: blue, red and white which is actual neutral. That is what your fan needs.

You wrote

(RI) Receiver In: white, blue & black

(RO) Receiver out: white & black

I think you have this reversed. The receiver controls the fan and light separately with inputs of white and black (neutral and hot, respectively) and outputs of white, blue and black (neutral, switched hot for light and switched hot for fan, respectively).

You could have only one wall switch provide input to the receiver and use the remote to control the fan and light independently. The other switch and its hot would be unused. If you mount the receiver on the wall switch, this might satisfy the requirement that there be a light switch on the wall. You could cover the unused switch with a shabbat light switch cover, e.g. these.

If you want to forego having the light controlled by the remote, and just have the light controlled by the wall switch (to satisfy the code requirement), you could operate the fan with the remote, and have the line hot to the receiver be the switched hot from the fan wall switch. But the blue output from the receiver to the light would not be used. Instead you would connect the hot from the light wall switch directly to the blue wire to the light. You can do this because there is a common neutral white in the cable from the wall to the ceiling box.