No, holes are real. Just as in a waiting line where sometimes "holes" form
for various reasons when electrons move they can leave "holes" of positive
charge(absence of electrons) that do exist. I don't like the use of the word
hole as it can easily be misinterpreted and actually somewhat hides the true
nature that is more confusion but should be understood.
These holes have mass in the sense of negative mass. That is, what mass
would it take to "fill up" the hole.
In a waiting line the gaps move always towards the back and the people
always move towards the front. If there is a gap that is formed then it
might look like it is moving forward but if you just look at the fixed
position of the gap and it will get filled by a person(but as that happens
there is a gap formed in front of them by the person in front of them moving
at the same time). We could ask what is the "mass" of a gap and it would be
the number of people that could fit in the gap.
For a np junction you can ignore the concept of holes but it does require a
little more thought. Since holes moving in one direction are equivilent to
electrons moving in the opposite direction you can use either concept. The
first one tends to be easier for most.