If you are creating a regulated 5V supply for the servos you can use that for the Arduino, too. Just hook it to the 5V pin.
That 7805 might not be the best chip for your conditions. This model can take up to 35V input and produce 5V at 2A output:
STMicroelectronics L78S05CV:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=497-1468-5-ND ($0.76 each)