All kinds of people can be a genius without formal education. People teach themselves trades and professions etc all the time

peer of whom, in what?

(i don't see a poll here. did you mean to add one?)

if someone knows stuff, who cares how s/he learned it?

but being a genius has nothing to do with that. iq is a measure of potential.

g

I think it depends a lot on the field. If for instance in the hard sciences the field relies heavily on empirical data and this genius makes hypotheses without any knowledge about the already existing established facts his contributions might be useless. In maths on the other hand some genius could come up with a new way of seeing things that nobody has ever done before, which could benefit the field very much.
It also depends on what you mean with formal education. Does reading the relevant material outside of an university environment also count as formal education or not? Then the problem would just be personal, the lack of connections and prestige that comes without the university education.

It probably depends on one's level of intelligence. If you define genius by IQ, then probably not for 98% of the population.