RSBM.
I have not personally heard of any U.S. national parks using CCTV in general and not for monitoring parking areas for criminal activity. I did do some Google searching, and all I could find about cameras in the national parks were 1) wildlife monitoring cameras at some parks and 2) EarthCams, which are like live feeds you can watch of some popular areas in certain parks; for instance, I think there is a live feed camera showing the Old Faithful area of Yellowstone. So IMO I really doubt there is CCTV footage or any sort of camera at the trailhead.
Also, the way the articles were worded were this: "Beyond finding Miller’s rental car parked at the trailhead on July 13, there have been few clues as to what might have happened to him,
except one witness who told authorities he saw Miller on the trail." BBM and taken from this article:
'Desperate for answers:' Sister of missing Canadian Paul Miller in Joshua Tree, retracing his steps
So even though I agree with you that stories may be vague, this definitely sounds to me like the witness is an actual person who spoke to LE and/or park rangers.
I still think an accurate timeline is important. I will say this and then stop harping on it (lol). Yes, his wife did say "around 9" and while that could mean 8:42, it could also mean he actually left at like 9:12, which would make Neil's sighting less likely to be Paul. Time estimating can go both ways (earlier than 9 and later than 9), so I wish we knew for sure what time he left, which hopefully LE has figured out from hotel CCTV. All MOO.