The walk ons are usually complete crap. However....it does depend on a few things. I had a walkon QB last season....no problem. He sucks bad. But.....I'm a running only team, so that guy plays on the running downs. No big deal. Many, many seasons ago I had a walkon DL that was actually halfway decent and ended up being the #2 All Time Sack leader (at the time) when he was a Senior.
You can always cut them, but your rep gets dinged for each cut. Which hurts you next recruiting season.