Procumbens nana has been a favorite of local clubs across the country for years. For a more upright variety, San Jose juniper has also been a fave because of their rugged trunks. For some reason, although it has beautiful foliage, Hollywood juniper doesn't seem to take to bonsai culture very well. Others may have a different take on that one, but that's my experience here and what I hear from others including Boon.
Zappa, Al (Smoke) made a pretty good list here at the bottom of page. Also to answer any questions whether a plant can go indoors on a semi permanent basis just look out your window. If it lives in the snow and cold then it needs a dormant period. So bringing it inside would deprive it of that.....which is not a good thing.
Im only looking to keep it inside during the summer.....I lose so many outdoor plants during the hot summer days....Ive been trying to properly balance my soil comp...my plants either die from root rot or underwatering...
By bring it inside it would only further your frustration by probably killing it. If your having a problem with the dog days of summer beating the snot out of your trees. I would suggest that the amount of sun they receive might be an answer for you. Partial shade or all shade in the hottest part of the year will do wonders. A tree, a shaded side of a garage, shade cloth, all will help you stop racking your brain on how to keep from getting root rot. BTW: what soil mix are you using that you have a real problem with root rot and how much are you watering?
I have seen it done with Procumbens nana by Jack Wikle for twenty or so years. However Jack is a gifted grower and uses a lot of sophisticated lighting systems and a good deal of TLC. Most of us mortal people would not succeed in this. I don't present this to be argumentative but to be accurate, yes it can be done. Can I do it? In a word No! Can you do it? Probably not. If you can't keep them alive outdoors the real challenge of an unnatural environment like in the house is probably the kiss of death.
You might try keeping them in the shade during the hottest months of the year, morning sun only and maybe some late afternoon sun. I think the probable culprit is that the pots are getting too hot. You could try sinking the pots in some natural Sphagnum moss, the kind you collect from the forest not the milled crap you buy at the nursery. This should help keep the roots cool without creating a moisture problem.
As to the root rot. Though it is possible the roots are rotting I suspect they are cooking. In the world of bonsai the standard caveat is to say it is root rot when someone describes an obvious root problem but sometimes it is not enough water and too much heat.