My poor benighted friend - you don't even know what a linking verb is (also known as a "copula), and you're waxing authoritatively on a grammatical matter. (And then there were the serial misspellings. Ouch!)

The verb "to be," from which the inflected verb "is" comes, is a linking verb - NOT a transitive verb. Linking verbs NEVER have objects, therefore the objective form WHOMever is incorrect. Rather, it takes a SUBJECT compliment, in this case WHOever.

It is for this same reason that, when answering the phone, for example, one says "This is HE" or This is SHE," NOT "This is him" or "This is her."

Does one say "WHOM is that person?" Of course not.

Last example...

"I don't know WHO he is, but WHOever he is, he seems pretty ignorant"

Get it?