If the goal is MUSIC, then to me anything goes (if it's musical of course.)
If the goal is musicianSHIP, it might be cheating.
I have starting using arps and/or loops quite a bit in my dance-oriented music. The arps/loops are just ingredients used in my musical soup, just like cooking.... if I use a Pet Ritz frozen pie crust for my pumpkin pie (which is SPECTACULAR, BTW), do you say I'm not a cook since I don't make my own crust?
I think if you can use an arp or loop in a creative, musical, artistic way, which results in a song that people want to hear, you have succeeded. Some people can't do that. Some can.
Listen to the very opening synth lick of this song:
http://www.youtube.com/watch?v=XJA6CXQI71U I could never play that. So did I cheat? But does it sound OK?
Peace, out. :-)