Hi,
What do you mean by customer contacts? Do you mean contact persons?
If that is so, using OB52 is surely safe. You do not have to use SARA for a customer which has not been used in a transaction. By a transaction, I mean a sales order or a sales activity or a material document. Invoices, deliveries are transactions too.
If you mean 'sales activities' by customer contact, well that changes everything. A sales activity is a transaction as well, so you cannot use OB52, you will have to use SARA.