I'm pretty sure the answer is yes, but I want to confirm.

I know that with the cardboard dials the faction doesn't need to match the faction of the ship card, but what about with the dial upgrades? Can I fly scum ships using the Rebel dial upgrades?

If you mean the plastic dial covers... Then no, that wouldn't matter any more than the cardboard top would.

You would need the correct ship icon I'd think but the cover itself shouldn't matter.

I don;t think this is specified anywhere in the tourney rules, but given that you can use any dial as long as it matches the ship, I can't see that it should be a problem.

There shouldn't be any problems. If you have the plastic covers then use them.

Cool, thanks. I figured not but it wasn't ever officially explicitly said (that I can find)

Tournament Regulations, page 3

Multiple Faction Ships

All pilot cards and ship tokens in a player’s squad must belong to the same faction. If a player’s ship has different versions in more than one faction, he or she may use any version of that ship’s model and dial in his or her squad.

The initial ruling was that all components had to match which meant Scum dials for Scum ships, etc. After a massive negative reaction to that ruling, FFG changed their ruling to the current one (above) which meant you didn't need to have Scum dials to fly Scum Z-95s, Y-wings, HWK-290s or Firesprays as long as you had the correct ship card and ship base token. The new dial upgrades are only a plastic cover, but the cardboard dial inside must match the ship type. And your opponent should be allowed to inspect them if he wishes.

When it come to dials it is important to know what maneuvers a ship should have avialable to it. In the event that a ship is assigned the incorrect dial if the maneuver revealed is legal for that ship (may exclude color but would be done as the correct color; need to double check) it can then perform it but if it is not legal for that ship then the opponent gets to choose a maneuver that would be legal for that ship.