All sources I've read stated that UV-light can only cause homolytic cleavage (homolytic fission), producing radicals while not mentioning whether it was possible for it to cause heterolytic cleavage instead. Hence is it possible for UV-light to result in heterolytic bond cleavage?
It is just a matter of energy of a single photon. Heterolytic cleavage of a symmetric bond requires more energy and can be less brobable, but see the totalitarian principle.
E.g. the extreme UV (tens of eV per photon) can indiscriminately cleave any chemical bond both homolytically and heterolytically.