VMware recommends SQL express for an environment with 5 Hosts and 50 VMs. But it may run without any issues if the configuration changes and performance statistic collected are less.
I would recommend to upgrade to SQL server Enterprise/standard edtion installed on a seperate VM or Physical machine. It gives more flexibiliy and greated administration features. Also it will support scalability incase more servers/VMs are added to the environment in near future.