HAwkeye has 2 ranged attacks, but does 0 damage. Seems kind of useless if you don't have someone to buff his damage.

However he also has RCE. This means he can use RCE only on one target for 0+2 damage, right?

If I want to use his 2 ranged attacks, then RCE cannot be used, correct?

You are correct; RCE specifies that it only works with single target attacks.
And Hawkeye can't get much use out of his two shots while he has 0 damage since the 0 would just get split between the two shots and do...you guessed it, 0 damage

Seeing Hawkeyes (E and V) wind up on both sides of a sealed booster game the other night, he didn't do nearly as badly under the new rules as I expected. While the two shots wasn't any use initially, the more limited mobility in the new rules made his 2 shots with incap clicks a little handier.