Hi,
In this regard, if SQL Server database is too big to operate and manage VMware vCenter Server, the database recovery model should be "Simple".
As you already know, after that, you'd better backup the database and shrink the data and transaction log files regularly.
I'll write Knowledge Base down just in case.
Troubleshooting transaction logs on a Microsoft SQL database server
http://kb.vmware.com/kb/1003980
Regards.