Most game companies have their own engine, only newer studios (created 2 years ago max) use ready-to-use engines, and most of them will go for unity because of license fees. cryengine is a risk because too expensive, only unreal would be a good idea to learn because the pricing is progressive according to sales. also its the best engine... of all time. just that. (the v4 that is.) and it will teach you the best technologies and practice, in terms of tooling integration etc... probably the best example anyway for a company with its own engine to aim at.
However, its not a question of resume.
Seriously, if I were to see the resume of a guy who brags with a list of "know engines" or "engines worked with" I would find that so lame that I would put the paper aside and see the next candidate.
If you want to say that you have experience with an engine, say it naturally in your cover letter.
But what is important rather, is having a general 3D knowledge. read the research papers ! when you know who is Kajiya, Nishita, Blinn, Kaplanyan, Rammamorthi, Torrance, Daschbacher, Hanranhan, Jensen, Schlick, Debevec, Perlin, Nayar, Lefebvre, Crassin, Neyret... and what is their work and all of their ramifications, then and only then you have conquered the knowledge that is necessary to continue this industry.
I insist that it is crucial to read on all of that, and nvidia research, ati research and stuffs like GPU gems and cie. not knowing an engine that will give you practice on the technology at a frame T in its history.
Also, games are not only a matter of graphics, but also specific game mechanics and tooling and various other production pipeline related stuff, and embracing the whole "corporate engine" is a plus because you can work more efficiently, in a huge codebase, thinking about human factors, e.g. not enforcing your own coding rules on everybody is an exemple of how to ease team work. Using diplomacy and politics to help the company move forward, when you want to make your project move from svn to git you're going to need those, I tell you...
I don't know how many hours I could continue on with that, but to sum it up all, I wanted to give you another perspective because you seem so hot headed and a bit stubborn on technology matters. C++ is great but my personal opinion is that game companies have already passed a turning point where C++ is becoming too expensive and a lot of studios died last year (more than 50) because of lack of clients of promising projects says the press. I believe its rather a problem of being too expensive because of C++. And especially the way it is used for game dev. it is enough to read the paper about EASTL to have a glimpse ! they code everything themselves for god knows what obscure reason. Many are predicting the death of AAA games against casual games. The CEO of crytek said himself that the upcoming generation of consoles is probably the last.
They are all responsible and they can only blame themselves, its not all because of C++, C++ is an awsome language, but the way game companies use it has a big role in this global decline.
I hope I gave you some perspective.