Probably will some, but need to use and additive to break it up and change it again. Some will run diesel Fuel in the oil for few minute to loosen up the sludge. Depending on how much oil it holds is to how much diesel fuel you add to get it to work.

Better to just buy the additive that's designed to clean the sludge or just use syn oil for couple changes and it should do the trick. Problem is how much wear has occurred from not changing the oil. Once you clean up all that sludge you may hear a thumping sound?

If I inherited that problem I would just use syn oil and change it twice with about 5 to 10 hours on the oil changes. then go back to syn blend oil. or straight 30 weight. see what others have to say?

I would recommend using Marvel Mystery Oil in your oil and gas. Put about two oz. in the oil. Use the mower several times or until the oil gets black and dump the oil while still hot. Put new oil in again and you should GTG assuming there is no damage from the low/dirty oil.
Change the oil at the end of each mowing season.