If we can run UTECs on modified STis, then yes, stock is safe. You have nice maps from TurboXS to plug right in for starters. It's a great way to start the learning curve. With a stock motor there's lots more support for you out there too... since all the stock motors are set up the same, and none of the modified ones are.
I'd install it, run it, and start reading everything from here, and wrxhackers and the UTEC tuners guide, and just let it slowly sink in. It's a lot at once to wrap your head around, but eventually you'll get to the point where you feel worthy enough to ask for help, and to almsot know what they are talking about. That's where I am now. I'm building a map for my car and it's progressing slowly, but it's progressing. I've mastered my fear of playing with fuel maps and delving into the timing map (the boost map isn't that bad at all)
If you want to get it down with the greatest of ease, get the tuner as well. I tried with the LM-1 wideband for a while but it was hard to stay motivated enough to combine the logs and really check the results well.
At any rate, don't worry about the UTEC. The support is out there. The product is great.