I worked for a 4Square supermarket and the owners sold out about 7 years ago. We were made redundant - all had to receive termination payouts which they had fairwork (or whoever it is) calculate those payments for the staff.
I was rehired by the new owners as were some of the other staff, however only as a casual not permanent, that suited me fine as I was earning more money and left soon to come to my current job, after anyway.

I think the new owners are well within their rights not to hire any pre existing staff as it is under new management and to be honest with you, it would be pretty negligent for them not to want to learn the bones of their new business - so don't be scared that means they are doing it to short shift you.