Hi,
Debian is a Supported guest OS for the vSphere.
But Installing vsphere on a debian machine..? ESXi is a bare metal hyper visor it does not require an Guest OS. If your planning to run debain machines on a ESXi then It is supported.
Please find the link for the same
VMware Guest Operating System Installation Guide,
Please let me know if this answers your questions or if I have understood the question incorrectly.
Thanks,
Avinash