Vader, Boba Fett and Tarkin are very good characters to farm, wether you use them on your arena team or not. They all command/pilot great ships, that are strong in fleet arena (unlocks at level 60). Furthermore, Boba is a scoundrel and one of the two—three MVPs for credit heist.
You will want to build a full team of 5 empire characters at some point to unlock R2D2 (and later Commander Luke Skywalker). RG is not the superman it used to be back in '16, but it will still make an OK addition to your empire team Furthermore, farming RG's hard nodes every day will not conflict with your other farming.
Empire work great in squad arena, especially after you add Emperor Palpatine, Thrawn and Tie Fighter Pilot (replaced by Sion/Nihilus at later stages). However, as someone already adviced, you should farm your Phoenix to unlock Palpatine and Thrawn, while still developing your arena team and pilots.
Other farm—worthy(tm) pilots, that won't conflict with farming Phoenix are:
Jedi Consular
First Order Tie Pilot
Biggs (a must—have pilot)
If you are lucky to end up in a young fleet arena shard, you may be able to keep a high rank for extra crystal rewards.
Good luck :—)