I don’t think so. I’ve been a fan of rap forever and can rap Eminem, Yelawolf, Tech N9ne, etc (sorry for the humble-brag) but I still stutter in speech. I think it has to do with skill transfer. Rapping does not mimic day to day speech. Rapping makes you better at rapping. For instance, the only way I improved my fluency talking on the phone was by talking on the phone. I got better ordering in restaurants by doing it. Skills usually don’t cross transfer like that. Strengthening your arms doesn’t make you a better boxer...boxing does.