Possibly

It depends, actual ballet flats used for dancing are soft enough and stretchy enough that the shaped sole wouldn't be too much of an issue- they also have a drawstring top. they will be very soft in the toe and heel and may not support the weight of the sole very well.
If the ballet flats have solid sides and soles then no, the sides will buckle and the heel support collapse inwards.
So if I can't find a shoe with the same profile of heel to toe in the sole then I will take apart some shoes for the toe and heel support and build up from there. If anyone buys these some shoes (or similar) and need to do the same I'll post my step by step.
For anyone with he right shoe but wrong colour it is easy to recover them and be neat and tidy:
pinkdiamond:
Not too in depth sorry but basically this shows my base shoe, the little repair and the final recovering of the base, all raw edges hidden
pinkdiamond: Tentacles get support!:The stuffing was
Mixed with this it shows how covers can look professional

Though admittedly I have seen some tidy but unfinished covers made for a tv costume.