Regardless of whether the omitted grammatical structure has a name, it's still skirting the intent of E-prime. If inserting the words "which is" has no obvious affect on meaning, then it should probably be a candidate for rephrasing.
Prescribe is a linguistic jargon. [0] It is exactly the correct word. And the whole point of E' is to remove is in such cases, because it carries an overloaded value which could change from person to person. In this case, a linguist would likely understand that it is prescribing a form of English, but not everyone would share that interpretation.
He, my bad then. English is very contextual. Point in case, prescriptive could also mean a speaker of E' must speak prescriptive. As foreign speaker, i then figured it means descriptive, which would've made some sort of sense to me, but is actually the opposite in linguistic terms.
Now I get down into semantics, can E-Prime prescribe something or is it the name of a rule-set that can be prescribed? I lean to the latter, hence my remark is still valid?
On another note, I find the recursion mentioned by OP quite interesting in a broader context. Choice of grammar has meaning itself.
Edit: Ultimately though, language is inherently underspecified, I heard, and I suppose in linguistic context it means a lack of definite distinction. You could go on subdividing prescription into negative and positive, i.e. prohibitive and, say, constructive. You could divide that ad infinitum. No?
> E-Prime, [which is] a prescriptive version of the English language, ...
That sentence should instead be written:
> E-Prime prescribes a version of the English language which excludes all forms of the verb "to be".