I've never seen a Vapor with a sheepsfoot blade. Not that there wasn't, I just haven't seen one myself.
There is a resemblance there, but to be frank, just about all knives made have a resemblance to one from another company. There's only so much that can be done regarding cosmetics of a knife, to make them look different.
Companies are finding their niches in things like different locking mechanisms,
different assisted opening mechanisms, serration patterns, blade steels, and whatnot.
China has no patent laws, so companies there are free to do or copy whatever they please.
I'm sure that it's not financially feasible for U.S. companies to engage in international law suits regarding U.S. patent infringement. If it was, they'd have done it a long time ago.
Also, with many U.S. companies using offshore production facilities, probably the same facilities making the "knock offs", perhaps they've decided that it's in their best interest to not push it too hard. If they lose the production of their "value" lines, they lose a big chunk of business.
It wouldn't be the first time that a company that does OEM work for a name brand told them to move on.
That's why the Okuma Fishing company was born. They did most of the OEM production and design work for Shimano. Shimano started dictating terms that Okuma thought were not in the best interest of their company, so they told Shimano to take their business elsewhere. Okuma formed their own brand and are now one of the cutting edge fishing tackle manufacturers in the world. There is a startling cosmetic resemblance in the many of the offerings from the two companies. The internal designs do vary, but Shimano, in essence, created one of their biggest competitors by pushing things to far. Okuma gains market share every year.