In a vacuum, tags aren't actually that important in the search results.
And yes it can be quite easily proved by looking at the tags of some high ranking videos for a given search term.
Here's an example that took me 5 seconds to find:
search term: "gta 5 flying school"
99k results
Front page, 5th result (for me) -
The video has one TAG (the channel name) - ""TheBrilliant"
If tags were important, he'd need at least one of the search terms in his tags right? Well he has NONE of them
tags are used mainly for 1)targeting ads to videos and 2)the suggested videos and then 3)a little bit but not that much in search results