As others have said, blocks won't hurt.
Here's some info that might make you think you don't need them though, other than convenience for attaching.
In the early 80's, I helped clean up my Grandpa-in-law's farm for an estate sale. Grandpa was a little touched; had been all his life. In the 60's, he bought a new large tractor and 6ft rotary mower. When he tried to hook them up together is when he found out his mower was 540PTO and his tractor 1000PTO, so they wouldn't work together as he'd planned in his mind.
So he parked the mower (don't recall the brand) in his pasture where it sat on the ground, uncovered for 20+ years. What was really bizarre was a few years after the purchase, he purchased a 50HP tractor that would have handled the mower nicely........
Anyway, to try to mow for the sale, I used the 50HP, went to the pasture, hooked up the mower, hauled it to the yard, and started checking it. That's when I discovered it had NEVER been used! The blades were brand new, other than rusted.
I checked for oil in the gearbox (yes, there was), and tried to hook up the PTO shaft, which was very stuck together. To finally get it loose, I hooked a come along to the front part of the PTO (while it was on the tractor) and the front axle of the tractor and cranked it tight. Then I'd go back to the PTO shaft (no plastic covers at that time) and smack it with a hammer.
I'd doused the sliding joint with pentrating oil and 20 minutes of bashing, it finally came apart. Cleaned the rust off, greased it, and put it back together.
Mowed like a champ for two days, then stored it in line with the other stuff to be auctioned off!
So, for NORMAL use, I wouldn't worry about sitting the skid shoes on the dirt.
Ron