Yes, Smackdown uses "canned effects" on a weekly basis to help enhance the crowd reaction for the televised product. This is something that WWE does as often as possible - constantly on NXT & Superstars, and in the case of a rare tapped episode of Raw. TNA also does this with episodes of Impact Wrestling to boost the sound of the Impact Zone. I have even caught both companies tailoring their audio for some of the newer DVD's that have come out.
My immediate reaction is to say "yes, it's incredibly annoying". Not only is it obvious to anyone that is paying attention that the reaction isn't natural, but it's an insult to the intelligence of the fans at home. I know they want me to react to Jindar Mahal, but nobody gives a crap! It's unbelievable when you turn on Smackdown and hear him getting heavy boo's...
On the other hand, you have to remember that these are TV shows. Number 1 goal: attracting viewers. If they DIDN'T have the canned effects, most of their shows would sound incredibly flat. You would be bored. People tuning in that have never watched wrestling would be bored. I think I would rather tune out the handful of times you hear the tweaked effects, and enjoy an exciting episode of Smackdown, rather than sit through 2 hours of Michael Cole commentary with a crowd that couldn't care less...
I will tell you, wrestling crowds need to STEP IT UP! The Impact Zone doesn't count, because it's a free audience. But I'm from Chicago, and no matter what the card looks like we get into our shows! I've never noticed doctoring of a show when it's coming from Chicago, and after being to over a dozen live WWE events in the city, I can tell you...big difference between Chi-town and most other wrestling cities. Same goes for Madison Square, anywhere in the UK, and to an extent Philly. You paid good money for those tickets, cheer for you favorites and boo the heck out of ANYBODY you don't like!