I have been loading 7MM Mag shells for over 25 years and I never worry about a slight dent here or there. What I do worry about is the number of times the shells have been fired (for me three times only) and also the load. I would advise loading to the highest load. I use the middle load for my shell and it gives great performance. The Hornaby shells are also excellent. I also do a thorough check of each shell every time it is fired. I use a magnifying glass to check for cracks in the casing. Any weak signs at all and the case is history.
But as I said before little dents come right out when fired.