I agree that it needs to be noted that Walker has not blown a save since getting the closer role. However, his three previous outings have been pretty bad. And although he only took one loss, all three games were tied when he entered and he allowed the deciding runs to cross. That's three straight times... He has earned some job security by not blowing any saves, but it's tough to know just how much. Personally, I think he has been downgraded to "short-leash" and I don't think he can afford many more bad outings with Hawkins in the pen.
To do: Watch his next two outings closely and if there is some shakiness, I would suggest picking up Hawkins if you need saves.