I've got answer from customer care:
"The standard database license pack with standard client will be sufficient to backup Exchange 2010 clients.
In NBU 7 because we only support snapshot based backups for Exchange 2010 we made some changes to the use of standard client and providing the backup uses the MS default provider or SFW then it will be fine.
If the customer wants any additional snapshot functionality such as IR or support for hardware based providers then they would need to purchase the Enterprise client."