Can't comment on the evolutions, but I've tapped the backplates on various OS, K&B, and ST in the past without issues.  The threaded part of the pressure tap will extend into the crankcase and will have to be ground flush with the inside of the backplate.  After doing this, I've just used some RTV on the pressure tap's threads.  There isn't a lot of metal supporting the pressure tap, but so long as you don't lever on the nipple putting the pressure line on, I didn't have any problems.  It's in an otherwise protected location.