DPS Parsers in Youtube videos.

[Fyce]

It's, in theory, forbidden. But in practice, I've never heard of a case where someone was banned for that (I mean, showing a parser in a YouTube video).

However, if he's caught in an argument with another player on the subject of "who sucked at DPSing", that other player can report him and give a link to his video, proving that your friend is using a third party software and was using that to parse the DPS of said player.
There have been some explicit cases of someone being whispered by GMs ingame on the subject of using parsers. Some got a temp ban if I recall correctly.

So, the answer to your concern is: is your friend 100% safe? No. Is he safe enough? Well, yes, to some degree.