Yes, they do not need customer deposits to create loans and increase their balance sheet, there are just some guys like you and me, putting the amount in the balance sheet and clicking save (simply put)

But yes, they need to have at least some customer deposists to make payments happen, since if they do not have any deposits, their central banking account would be empty, therefore none of your loans could actually leave your bank since the transaction wont happen. (i'm talking from perspective of TARGET2 / ECB / EURO system)