My friend shaves(or clips down?) his sheltie every summer with a 0.3mm length shaver. He's lucky his dog genetically has a lot of coat. But I notice his coat is much lighter when it grows back and also gets mats very easily. The guard hair does not finish growing in a year before its clipped again. He said shaving him down really helped with the panting. I guess less hair means the dog can cool down quicker so it does make a difference?
I have yet to clip down my boys, but I always make them wear cooling vests when we go out and we avoid walks during the day.
If by shave you mean all the way to the skin then I would say no. But if you can clip it down short I think it's okay. But personally I cannot live with the fact his coat might never be the same again. But my friends sheltie like I said still grows a lot of the undercoat back, maybe he's lucky? Lol I'm not willing to take that chance though. But according to my breeder as long as the you don't hurt the follicles by using a hot blade it always grows back.