Not that i've trained to do it, but I've managed to accomplish this once with the machete, partially out of desperation and mostly due to lack of options with a fleshpound in my face.
I think it's a feature. All Zeds have weaknesses in general. I can kill crawlers with a melee weapon when they jump, before they even hit me. If you get into extremely close range with a siren, they only bite you for very little damage (assuming no one else is in her screaming range and you aren't constantly shooting her, she will get one scream off), making charging a siren with an axe a perfectly viable option.
Everyone knows you shoot a bloat in the mouth with a LAR or two and it goes poof, scrakes can be chain stunned with powerful enough weapons (if you think it's a glitch, look at how gorefeasts and clots react to an axe or machete power hit they survive, they get stunned (and those would be their weaknesses if you even bother to need em).
And stalkers, you look for their shadow, and they reflect the flashlight pretty well.
Each zed has a tactic, with it's own pro's and con's. Why shouldn't the FP?