The major issue is how do scholars qualify a shaved man?
So the majority of scholars consider a shaved man as fasiq and that shaving the beard is haram, but a saghira (minor sin). While shafi'i scholars say it is only makroh. And their major evidence are ahadith like this one from sahih al-Bukhari (can also be found in sahih Muslim and Musnad al-Imam Ahmad) and this one from sahih Muslim.
A fasiq is somebody who has committed a major sin or performing a minor sin (more or less) permanently.
Now that we cleared that the majority consider a shaved man as fasiq, we can check, what scholars say about praying behind a fasiq:
The majority of scholars say that it is makroh to pray behind a fasiq.
While the hanbali scholars and one of two statements of the maliki school is that it's not allowed to pray behind a fasiq.
Now who is the best person to lead a congregation: a hafidh/hafiz or a man of knowledge. The majority of scholars say it is always a man of knowledge, but hanbali scholars say it should be a hafidh/hafiz.
One could conclude from all of this that among sunni scholars it is -at least- considered as makroh to pray behind a shaved Imam, as he is considered as fasiq. The shi'a view can be concluded from both the answer of our brother Zia and the comments of brother Ali on it.
For further information (see this fatwa and this one from the Saudi Arabian fatwa council in Arabic).
A special case is an child Imam, this means if for example a boy is hafiz/hafidh, most scholars accept him as an Imam for nafl/sunnah prayers (taraweeh for instance).
Also note that the fatwas refer to man who shave their beards, not for those who don't have a beard for natural (given by Allah) reasons or in case of a very slow growth.
And Allah knows best.