My son is rostered on an Ivy league team. There are no JUCO transfers on the roster.
Looking at the larger student population, it is very difficult for ANY student to transfer into the school. There are approx 1050 new students (freshman) admitted each year. The annual student population is generally static, 1050 graduate & 1050 are admitted. The only chance a transfer student has to be admitted is if a resident student chooses to leave the school, opening a spot in the class allotment of 1050. This is very rare, though I am aware that it has happened.