Is there a huntable population of elk in these mountains? If so, then I would bet every dollar I own that there is not a population of grizzly bears flying under the radar.
Grizzly bears just aren't animals that are able to fly under the radar. If there's an elk hunting season, then there's a shit load of trail cameras out there every summer that would have real proof, and not a grainy digiscope picture.
Grizzlies populations are expanding in MT right now as we speak, and you can basically watch in real time as confirmed sightings follow these bears in to territory they haven't been in 100 years-
https://www.kpax.com/news/western-montana-news/grizzly-bears-seen-in-more-western-mt-locations
And this is in an area with a fraction of the human population that Colorado has.
And come on, what are the actual odds that the first confirmed sighting would be by a poacher from Australia who has built a career off of drawing attention to himself?