The answer is simple: no, a priest cannot deny absolution simply because one is an “uncatechized” Catholic. The Code of Canon Law says,
Sacred ministers cannot deny the sacraments* to those who seek them at appropriate times, are properly disposed, and are not prohibited by law from receiving them (Can. 843 §1).
“Uncatechized” Catholic is simply not a Canonical category, and so, on principle, such Baptized Catholics cannot be denied Confession or absolution.
Of course, to receive absolution, a person needs to be truly repentant and have a firm purpose of amendment (i.e., make the decision not to commit the sins confessed anymore), but that is the requirement for everyone.
As far as the validity of the sacrament, if the priest did not give absolution, then, unfortunately, there was no sacrament.
My suggestion would be to go to a different priest, and explain the situation. It would also be necessary to confess to him at least any mortal sins (those that one can remember since the last valid confession), in number and kind.
(As a side point, I would encourage those Catholics who have not received confirmation to look into receiving it. Confirmation completes the initiation that was begun in Baptism and gives them the strength of the Holy Spirit.)
* In this context, the law is referring to the Sacraments that the baptized faithful need in order to be right with God: confession, anointing of the sick, matrimony, confirmation, and especially the Eucharist. Holy Orders is a bit different, since it is never necessary for one’s personal salvation or friendship with God. The Church is never under an obligation to ordain someone, and, indeed, is gravely obliged to ordained only those persons that, in her judgment, really have a vocation to the priesthood or diaconate.