Danny Danzi
I say everything is a "go" if you need it. These tools were made for people to use and if it gets your idea out of your head to where you like what you've done, you made the right choice.

Now, me as a guitar player....I literally play arpeggios in my lead passages. If I were not able to play one up to speed and decided to play the passage extra slow and then have the computer speed it up so it sounds right, I'm cheating and it's unacceptable to ME. If someone that doesn't play guitar like that decides to cheat and do it, by all means it's acceptable...as long as they fess up and say "hey, I wish I could play like that but I can't....so here's what it would sound like if I could!" :)

-Danny

That's pretty much how I feel as both a Bass Player and Guitar player.  If I can not actually play it live, then I feel I am cheating.  At the very least, I am cheating myself.  There are many solos that I have had to practice parts of for more than a few takes, but I want to be able to say I could pull that off live.  Why, because I might just have to on one of the gigs.  

If you have to ask, it's cheating.  Ha ha.  Of course it is.  You didn't play it.  And neither did anybody else.  And that's that.  No amount of rationalization will change it.  Did you give the ARP credit for its performance?  
 
I've cheated quite extensively in the past when I was struggling to be able to play.  Lots and lots of strategic punch ins and outs.  Then I'd do these logical contortion exercises..."this isn't cheating or anything, no, not at all...the computer isn't even recording my whole guitar anyway...just samples of moments of time..yeah...it's not really real anyway...my computer is generating the sound...ooh good one...all sound is computer generated at the end of the day, ya know?  nothing to see here.."  
 
I never worried about cheating on my homework in high school and I won't lose a lot of sleep cheating on my little songs that next to no one will ever hear.  
 
 
 
 

roger fisher of heart, used an arp avatar, 
i never thought that was cheating!
 

It depends on the music too.  If its quantised electronic music then arps fit in rather well.  You can still put a lot of creative expression and make them your own by how you actually play the keyboard parts with the arps switched in.
 
Then even live playing over quantised material sounds good too.  Live playing audio can so easily be quantised to fit the sequenced music.  So many options.  Midi parts can be humanised to make them feel more live.  Both midi and audio can be anywhere between live relaxed playing and everything perfectly tightened up for quantised parts.
 
 

It's only cheating if you need a shower when you're done.
 
 

It's only cheating if it's a competition. ;)

Like a few people mentioned, it's a means to an end. If this is what you need to make your vision of your art come to life, why not use it? No different to saying "sing with less dynamics and don't make the sibilance so pronounced and give yourself a certain tone" instead of using the sonic characteristics of a mic > preamp > compressor > deesser > EQ to record a vocal and make it sound the way you want. It's all cheating in some way unless you're standing in front of a person as they perform unplugged at you. Where do you draw the line?

nothing is "cheating"!