I would agree that witness marks would be a fine solution for light carry use, or use during shooting matches . If that's the scenario where these are going to get used, then I wouldn't worry a bit.
However, as a hunting bino that come in and out of a chest carry case (or no carry case), and get bumped around while moving/hiking...I couldn't deal with bringing the binos up expecting a clean view and finding the diopters out of whack. Having to stop and re-focus (even with witness marks) can mean losing the precious few seconds needed for a range or confirmation of legal vs non-legal animal.
As any elk hunter knows - that shit can happen fast. You often don't have more than a few moments to grab a range, confirm your target, confirm legal animal (or specific animal if you have one ID'd), then get in a position to shoot.
Now, its likely that Sig made these for shooters, not hunters. Primarily for matches, use on tripods, etc. And if thats the case - then using witness marks for the diopters won't matter. But as a hunting bino...non locking diopters is a no no, at least in my book.