Split verbs do actually exist in modern English. Schoolmarms may enphatically teach that they're flat-out wrong, but linguists have long maintained that English rules of grammar are descriptive, not proscriptive. Actual common use is what is considered to fundamentally dictate the rules, not vice-versa.
I'm not sure, but I think you're confusing split infinitives with split verbs. Split infinitives are definitely a schoolmarm invention (borrowed from Latin, where the infinitive is an inflection and thus inseparable). I think split verbs are here referring to the possibility of separating verbal auxiliaries from their verb.
I think by "split verb" he's referring to "separable verbs", where a particle, resembling a preposition, moves to the end of the sentence. This sometimes occurs in English, apparently violating the "schoolmarm" rule to not end sentences with a preposition.
The concept to which you're referring is that linguists describe language without shaping it. Its like saying scientists don't make physics, they observe it. With sociological phenomena the distinction between dictating something and measuring it is finer, but it doesnt mean linguists hate prescriptive grammars.
