As for the likelihood of Warspite's attacker wearing this Wave Mirror camo, I am all but positive this one came well before the later, night-fighter (black-over-gray) patterns - ultimately coming factor-painted, as feathered blotches - which you are probably thinking of. The earlier, field-sprayed "squiggles" - and particularly the light-oversprayed, Wave Mirrror treatments, which could well have come yet earlier still - were documented for aircraft in southern Italy, which was all a done deal by 1944. And as for the aircraft themselves, remember these are the Dornier 217s - not the earlier '17s, which they were specifically designed to replace - due, as you rightly point out, to the '17s withdrawal as obsolete/inadequate, after their decimation over Britain, etc..
So I'm pretty well convinced that this aircraft, this camo scheme and the attack on Warspite all coexisted in the same place- and time - and even could well be accurate for the particular aircraft in question (though I didn't find a single picture of any plane from Kg100, which was its Group).
Of course, per my philosophy I wouldn't let any minor historical inaccuracy(ies) stop me from completing it the way I find most attractive/interesting, in any case.
So, stand by for results of my "squiggle research" - which I'm already taking pics of, on my bench, even now - and thanks again for the encouragement, Gus!