(My Latin is very rusty. Take all of what follows cum grano salis.)
Why tenet rather than habet? (I expect I'm revealing extreme ignorance here.)
"Nothing" isn't quite the same as "nothingness". Perhaps inanitas?
Literary Latin tends to be rather terse. I wonder about removing the verbs, producing something like: "salvator sine salvatore. propugnator sine dominum, sine matre, sine patre, supra solum inanitas." but that may be too far from Eliezer's English version.
[EDIT: I also wonder about "soter" rather than "salvator". It's not so common a word in Latin -- it's simply a transliteration from Greek -- but I think it sounds better :-). On the other hand, I don't know what they'd have used for its ablative.]
[EDIT: Wouldn't "salvator salvatorem non tenet" be better than "salvator non salvatorem tenet"?]
Why tenet rather than habet?
My feeling with those words is that habet mostly refers to actual objects, in a mundane sense (e.g. "I have a fork"), while tenet is more of an abstract "have" (e.g. "I have a belief").
If anyone can do non-wrong Latin, I could use a translation of the following for HPMOR. The original is supposed to be circa 1200.
No rescuer hath the rescuer.
No Lord hath the champion,
no mother and no father,
only nothingness above.