Marmoset uses the same lighting tech as other engines, even if it's not a "real" game engine, it will give results similar to other engine people might not have access to for portfolio projects.
Marmoset Toolbag 1 is most certainly a game engine, we even made a crappy game using that engine (marmoset engine, game: Darkest of Days). Toolbag is simply the rendering component without the gameplay component. Unless you're specifically intending to demonstrate gameplay, Toolbag 1 is no less a game engine than UDK,…
From what I think, marmoset started it's life as the game engine for darkest of days. http://en.wikipedia.org/wiki/Darkest_of_Days It's more aimed at presentation instead of game development, but it still shares a lot with complete game engines.
anthony vaccaro (autocon) is a portfolio that springs to mind: http://wireframeworlds.com/index.html and most of the images in my portfolio are screenshots from a game engine http://dankeating.wordpress.com/
that kind of distinction is ridiculous. models being shown in UDK are no different to those being shown in Marmoset. you have to do all the same things in both cases. Marmoset just had the game part stripped out, it's still the same core engine and renderer. i mean what exactly do you think the difference is? that you…
Also it's pretty easy to find art made in UDK, Cryengine and Unity, look at all the games made in it, there is plenty :) Here is a great portfolio with scenes presented in cryengine among other engines. http://www.helderpinto.com/
It doesn't matter which engine it's using. All that matters is that it's running realtime instead of via an offline renderer (vray, that kinda shit). You can use the fricken viewport for realtime shots if you can make it look nice.