CPU management is quite real time. Actually CPU time is divided into 20ms quantums (iirc). So whenever there is enough idle CPU things are going to be relatively fine.
In the case there was a contention for CPU between the DB server and other VMs someone is going to win and someone is going to lose.
You can play with several factors: minimum, maximum and shares.
If you don't want the DB to disturb other machins you can give it low CPU shares, or give it a maximum CPU time.
If you do want the DB to have high priority you can give it a minimum reserved CPU time, or high shares.
Another advice is to not give VM too many vCPU, as it may be counter productive. In the worst cases even having idle physical CPUs the system may not be able to schedule the VMs. You may notice this because of high "co-stop" values in performance charts.
Also, if you have DRS license you can give the DB VM some minimum CPU reservation so the system tries to pace that machine on an ESXi that has enough spare CPU.