We would like input on short arm suspension lift kits. We would like to use our stock rims, how safe is it to use a wheel spacer if required? Or should we rethink and buy new rims?

 

Spacers are perfectly safe as long as they are hub-centric like the Spidertrax spacers, and are torqued properly. I installed them on my previous JKU, a 2010 which was lifted with 35" tires and stock wheels, and have them on my 2014 JKUR with stock suspension wheels and tires. On the stock Jeep they give it a wider stance and feels much more stable on turns.

 

I think the general thing to keep in mind when using spacers is that you will have to spend considerably more time on preventative checks. They are safe as long as you take the time to check them regularly, and this involves removing each wheel and checking the torque on each spacer at at least every oil change interval. I would also recommend checking them after any trip out where you used 4WD extensively.
It's probably a good idea if you can get 5 spacers, one spare just in case, if you do a lot of wheeling. You wouldn't want to be stuck out on the trail due to a cracked spacer and not being able to get your wheel on. When you start considering the cost of getting 5 spacers though, you can certainly find wheels that cost the same as those spacers. They might not be most stylish, but they'll get the job done and avoid having to spend the added time needed to properly check the spacers.
I do like the stock wheels though, painted black, they are pretty good looking.