Hey Sharp! Well, anytime you are on the ice, you should always be on alert for large cracks, especially pressure cracks, other people on the ice, weather conditions, ice color, etc. As for putting your tire or ski in an old hole, most augers used to fish through the ice are 6 to 8" in diameter. There are some who use 10", but for majority of fishing here we usually see 6 to 8". The holes do freeze back over fairly fast, but even left open, the size of our tires on these Pioneers just roll right over those size holes.
An exception would be holes used for spearing, which can be several feet in length and a couple feet in width on average. That could do some serious damage. I have many years as a member with the dive team for our local sheriff department, and we would cut large triangular holes for access to the water large enough to get the diver in and out of water. If the spear fisherman use the same tactic that we on the dive team use, then you should be able to notice the hole as you approach it.
After we cut the ice out to access the water, and upon completion of our training or mission, we slide the ice chunk back into the hole, and mark the corners with tall stick and sometimes yellow tape. It doesn't take but a few hours and the large chunk has frozen to the surrounding ice leaving a nice flush sheet, and for the most part, unnoticeable.
However, many spear fisherman around here aren't so kind, so not only do you have a large hole that needs to freeze over and the ice is dangerously thin for possibly days, you also have the large chunk of ice which they pulled out and left on the ice that freezes to the lake so in effect, if struck, would be like hitting a large, and almost invisible, concrete block. We don't get alot of spear fisherman in my area as they usually go for a specific species. But nonetheless, one more thing to keep your head on a swivel for when out on the ice. Appreciate the question. Hope this helps!!