Rich:
I can't say anything about what you're describing at Royal Dornoch because I've never been there.
But actual grass covered mounds (and chocalate drops) are not convex bunkers. Actual convex bunkers (with sand not grass) do exist, although they're quite rare. There is one or two to the right of the fairway on #9 NGLA, where all the sand is above the grass covered surrounds.
Mounds, though, are just another kind of architectural feature and you're definitely right they have gone out of favor these days--at least the type that are the smallish individual mounds of some of the very early courses of the late 19th and early 20th century. Mounding, though, as you know, has been used and over-used in the form of "containment mounding", the identifiable design feature of the previous career of Rees Jones; we really don't want to go here though, particularly since he's very much changed recently and gotten beyond that fetish and into much more natural and site specific type of architectural features!
Originally though grass covered mounds came about in architecture not unlike bunkering itself came about in golf--for another reason. As original undesigned bunkering was natural wind and water created links formations or the work of sheep burrowing into the lee, mounds on golf courses originally were areas of debris cleared from the course (whether rocks, stumps etc) that were piled and covered by sod and turf as the debris was too costly or cumbersome to move or remove.
Architects copied this original grass and turf covered debris in creating mounds just as a design feature but it certainly never caught on to the extent that bunkering did as a necessary golf feature. Ross, Tillinghast and some others did quite a bit of it. Sometimes they even combined mounding and bunkering with what they called the "cop" bunker (a small bunker in mounding).
The real old "chocolate drops" looked really artifical and for that reason obviously didn't survive in architecture. I like mounding occasionally but it too is sometimes hard to make look natural. Coore and Crenshaw have done some small mounds and mounding recently though!
But I think it would be a real stretch to try to call any type of grass mounding convex bunkering.