Single status means same terms and conditions for all levels - so if they provide perks such as a car park/healthcare/canteen it should be equal access for all regardless of mgmt level.
It could well be that the single status rule applys only if you are a permament employee and so to get round offering all staff the same perks they have made some jobs short term contracts (even though they will always be renewed.) This way they do not have to give everyone the costly perks but have not had to scrap single status which would be unpopular.
Best check with your union rep or ask your new line manager.