Almost all airlines have a long sleeve option. INCLUDING EasyJet's new uniform!!! BA, QF, NZ, VS, BD, EK, JL, NH, CX, EY, QR... to name a few.
If it can't be seen when in uniform, you should be fine at most airlines.
The inside of the arm, is becoming a very popular place to have a tattoo these days. I know at least three people who have one there.