will my vSphere 6.0.0 still be able to attach and load my VM guests?
The "fat" vSphere client is already deprecated with ESXi 6.5. You would use the ESXi embedded host client by entering at your browser
https://<esxi server/ui
You can also use the host client with ESXi 6.0
https://labs.vmware.com/flings/esxi-embedded-host-client
will the newer ESXi 6.5 or ESXi 6.7 corrupt me 6.0 VM's
No your VMs will not get corrupted. But if you are concerned about it, for peace of mind, have a backup of the VMs.
It is a good idea to upgrade the virtual hardware compatibility of your VMs if you want to make use of certain features. For example, version 13 (ESXi 6.5) supports VM UEFI secure boot and virtual NVMe controller. Also higher virtual hardware version exposes more CPU features to the VM(s) if the host CPU is new. Do note that ESXi 6.7 drops support for Nehalem and certain Westmere CPUs. Look at the release notes of ESXi 6.5 and ESXi 6.7 and check the VMware Hardware Compatibility List.
https://www.vmware.com/resources/compatibility/search.php?deviceCategory=cpu
do i need to also update vSphere 6.0 to 6.5 or 6.7 respective of ESXi version?
The embedded host client replaces the vSphere 6.0 client.
