I think it really comes down to you design and if virtualising it is worth it.
I have not seen anything official saying virtualizing vcenter is prefered over a physical or its best practice, i think its more of a why not, can do it now maze well. and VMWare being in the business of virtualizing then im sure they would recommend it.
I have a mix of physical and virtual vcenter servers and i can say the virtuals ones are far easier to recover if there is an issue, just have to make sure you note down which host its on in large clusters. all the issues you mentioned can just as easily happen on a physical box, and nothing is stopping you monitoring a virtual vcenter server.
Personally i like the physical i know where it is i can touch it and if an ESX host dies its still up and kicking. but having worked with both and suffed failures with both i way prefer 5 - 10 minute recovery of a virtual vcenter server over sourcing a new physical restoring from backup etc.