I suppose that's possible, but based on the fact that the paintings seem to be mash-ups of different pre-existing robot designs, I'm more inclined to think that they are fan-made. Although the Japanese have no problems with "recycling" ideas from other sources, it would be unusual for a company like Takara to try and pass off such classic robot design elements as their own.
Lets look at this one next:
The robot arms, upper body and the jet alt mode look like they were taken from Dangard Ace
While the legs look like they were based on Dragonar (or some similar robot featured in the Dragonar
The head is generic enough that it could be original or merely any existing robot with a face-plate added, for example Jet Robo from the Machine Robo
So IMO, those paintings were done by a giant robot fan who knew enough to mix-and-match different robot parts from existing designs to create the appearance of an original design, but none of those are truly "original" robots.
I used to do the same thing when I was in school by picking and choosing elements from different Japanese anime art books and drawing "new" robots. It's a fun exercise, but not the kind of thing you'd expect to see put out as a licensed Takara concept.