Nothing wrong with clipping a dogs coat in my view. It doesn't ruin them either. The hair is simply cut short, just like when you cut yours, and it grows back.
My mother in law cut her Border Collie's coat every year and I have had so many people tell me that it would ruin the coat. I beg to differ. Tasha had the most glorious coat and it always grew back just as lovely.
Zen, you won't have ruined Nelson's coat. You've done hima huge favour getting rid of the matts though!
Vellela, if Ollie's coat is as thin as you say then clipping it won't help with the heat I wouldn't think.