Yes, you can expect modern games to use any and all tricks available to squeeze performance. Imposters are an example of a LOD (Level of Detail) technique, which is standard in all game engines.
"The engine also used two other big tricks to lower the poly count: The most famous was "object caching": While rendering objects, the distant ones would be rendered to a cache and drawn as sprite on a quad. This trick originally resulted in mixed results since the mesh would remain a sprite too close from the player and changed from 2D to 3D in a very noticeable way as see in the two next images" (http://fabiensanglard.net/trespasser/index.php)
There are also tricks using a lower temporal resolution - for example giving fewer ticks per second to the logic or animation of entities further away/out of sight.
It functionally works as a different game. I watched an ex play through the whole game on PS3 (her choice) and there were many aspects of her playthrough that were not tied to her platform, but were hindered by being on the PS3
Billboards that are used as substitutes for 3D models at long distances are more specifically called "imposters".
BTW I've often noticed these 2D images (which work better than I'd've thought)... but for distant objects (in an open world game where the player can approach them from any direction), is a 3D model ever rendered once to a 2D poster when the player first sees them, then that is reused (until player gets too close; or approaches at too different an angle)?
I'm concerned at the uneven computation required as objects move in/out of range and need to be re-postered. (I prefer steady fps).
Similarity Super Mario Odyssey has lots of clever tricks to hit 60 FPS. For example far away models animate at 30 FPS instead of billboarding. You won’t notice it because there’s so much detail and richness close to you.
On the other hand Just Cause 3 barely manages to keep above 25 FPS on a standard PS4. The difference is jarring.
As a side note the a Fox engine used for MGSV was also used for the P.T (Playable Teaser) for the cancelled Silent Hills. This was incredibly photo realistic and pretty scary!