If Symantec supported every whitebox in the market they would have to support some really obscure cheap stuff, and the phhowe17 nailed it, it would be a support headache.
I'm typing away on an AMD powered box that uses a VIA chipset with a 10/100Mb NIC from also from VIA, called a Rhine II. Then there are Nvidia NIC's, so on and so forth.
By supporting ESX (AMD based NIC from the 90's) and the Dell based config (probably an intel), they can better control the environment the product is install into.
Get a desktop and install ESXi, and see if that'll do.