Is it safe to massage someone with spondylolysis ?

Yes: Quite safe support from hyperextension by placing a pillow under belly while laying on stomach for massage most comfortable idea.

Yes : Yes -- there are 2 types of this condition. One is known as congenital which usually is noted as early aa age 5 but more toward teen years that can be more of a stress fracture associated with higher level active athletes. Massage is fine. The other is due to a true trauma that could be associated with an unstable fracture & may not be approprate for massage until it has healed.