Diff-hardening 3V is possible (it's been done - sort of - with D2; look up Dimaond Blades Friction-Forged knives) but it would be crazy expensive and frankly not worth the effort. "Normal", through-hardened 3V exhibits very high toughness and very good abrasion-resistance... which is precisely what it was designed for.
This may not apply to 3v, but in my CNC manufacturing classes, I learned that heat treatment can add stresses and distortions to a ground and shaped piece of steel.
Grinding afterward would seem to make these distortions and stresses in the final piece moot, as it still has to be ground to shape yet anyhow.
Yup, all the same principles apply. As mentioned above, it's not nearly as big of a deal in a piece as simple as a knife blade, as it would be in a really complex part.
But it can still be a major factor on really thin sections, like the edge of a chef's knife. On those, I routinely grind modern tool and stainless steels like 3V and CPM-154 right down to final dimension, with an edge of .010" or less, ready to hone,
before HT with no problems... if I do the same with simpler steels like O1 and 1095, they're very likely to end up with an edge that looks like cooked bacon (warped/wavy). That's one of the reasons alloys like chrome and moly are added to high-end steels - to increase stability during hardening and especially during quenching.
HT then grind sounds like a rather difficult way to get things done. Why does Survive do that?
BRKT and most other manu's do the same. It's faster and less costly in the long run, mainly because it cuts down on procedural steps and shipping, and possible warping of thin edges/tips during HT. Simply have steel sent to a laser/punching/waterjet firm, have them ship the blanks to the heat-treater, have the hardened/tempered blades sent to your factory, grind 'em, build handles, done. (The only way to be more efficient than that is to do everything in-house, which is cost-prohibitive for smaller manu's. Larger companies generally follow the same overall process.)
It's a perfectly legitimate way to make knives, when it's done right. The only problem comes when the hardened blades are ground too aggressively, resulting in over-heating the edge and fouling up the temper... which unfortunately happens fairly often.
Probably 8 times out of 10 when people freak out over a certain "batch" having "bad heat treat" and not holding an edge like they should, what really happened is they got hold of a few examples that were over-ground. When you rely on either robots or humans who are programmed/paid to crank out X-number of blades per shift, that's gonna happen sometimes.
You can find lots of videos from TV programs like "How It's Made" that show the whole process in 15 minutes.