IMO a third party could only conceivably be involved at the cedar and ravine, because in those areas the later snowfall would cover their tracks, it would tend to collect at lower elevation rather than be wind scoured, and we know what fell lower down the pass from the way it covered 3 bodies under approximately 2ft of snow in the weeks before the recovery team found them and how the hiker tracks disappeared halfway to the forest. So Mother Nature would erase half the crime scene.
However, in order to flush the hikers from the safety of their tent at 3000ft, a third party would need to scale the pass to that elevation, and that means, as with the hiker prints around and leading from the tent, the risk of the third party footprints also being preserved.
I suppose, if you were determined to cover up your crime, and braving the cold for a prolonged period of time, ensuring that no witnesses saw you or you'd need to murder them too, that you could either dig out your compacting footprints and backfill with soft snow, or do some vigorous raking, in what would in places be deep snow. And you'd need to do them all, being unable to predict the forthcoming weather so that you couldn't be sure which prints risked remaining. Where your footprints intersected the hikers' on the way down it would be virtually impossible to selectively erase yours and leave theirs so that there was no suspicion the tracks had been tampered with.
A man typically strides 3ft, less so when in snow of varying depths, or when on a slope, so let's say a 2ft average stride on that mountain = he has 2640 footprints to remove across 1 mile if approaching the tent from the cedar/den, and the same again back down = 5280 footprints which he cannot rely upon the weather to hide in whatever unknown time will elapse before the bodies are found. And that's not even including footprints leading to and from the general area.
5280 prints is just one man, who presumably would need a gun to get the unarmed hikers out the tent and off the pass, or a larger group without guns but intimidating enough to overwhelm a vulnerable group, so let's deploy a minimum of 4 burly men with knives = 21,120 footprints, any one of which might be as incriminating as if trodden into wet concrete.
Either way that would be some clean-up job.