Peteroo; You're making this way too complicated, if you'll pardon me for saying so.
You're absolutely correct in suggesting a collet nut coming loose is not a good thing, but having agreed with you on that, no, don't put oil anywhere near the collet assembly
! keep it clean of course...I use acetone to wash nuts and bolts in if I don't want residue left behind. Wiping it down with Mineral Spirits (Paint Thinner) would work just as well...but no lubricants and no WD40.
As for the wrenches, have you lost the ones that came with the router? The nut only needs to be firmly tightened, not reefed down so you have to fight with it to get it to release.
Have you already had a bad experience? What prompted this concern about the nut coming loose??? (Not that being safety conscious isn't a good thing!)