I think its always good practice to separate OS from Data. In this case Proxmox is the OS and the VM's the data.
If the root drive dies you have lost your VM's - and if you do not have a good backup strategy you are not in a good place.
If you have VM's on one drive, proxmox on the other, you have at least made it possible to reinstall proxmox and still have the data for your VM's available.
And also consider that proxmox when its running will not write a lot of data on your, but if you put VM's on the drive you are putting more stress onto the "important" drive for your VM solution.
It is certainly true that for a homelab many of the good practices does not matter much - but why not practice stuff that is considered best practice - even if its a hobby and you only have small requirements.
A disk can die at any time and if you put all your eggs in the same basket you are making it harder for your self.
Obviously you should also have a backup strategy in place.
So yes, anything goes, but you can buy a cheap small SATA ssd and put proxmox on that and would probably not have to worry much about it being worn out.
Small enterprise SSD's are cheap.