It is possible that RF feedback will impact your CW signal, but obviously much more rare than such occurring on SSB.
There won't be any screaching or howling, though! RF feedback on CW can result in leading or trailing edge issues, making the signal sound choppier (too sharp an edge) or "mushier" (too soft an edge) than normal, keying transient overshoot (which sounds lousy on the air), and -- the most obvious symptom -- having the transmitter "hang up" and continue transmitting, even when the key is opened and the transmitting should have stopped! RF can get back into circuits that can affect operation in many ways...the PLL/synthesizer circuits, which can make your rig change frequency or create a "chirp;" the VOX circuits, which can cause it to "hang up" as described; the flash memory devices (if any), which can cause memory erasure and other ills...oh, gosh, lots of places!
It's definitely best to eliminate RF feedback problems prior to operating...and they are easier to find with the microphone connected, usually, because they become so obvious!
73 de Steve WB2WIK/6