Personally I think it's inapropriate to judge after one's rank, I think a rank is a good paramater to keep an eye on and I feel like high-rank players should be given somewhat of a priority based on the fact, they know a bit more about the game - and I know people can say, "that no high-ranks are not good, I'm as good as them but I just am not a nerd that nolifes nonstop", but as somebody who plays league and achieved relatively high rank (diamond EUNE and plat EUW), I can tell you that's a sorry-ass excuse. Rank does matter and while your game knowledge may be on relatively the same level, it's the small details that make high-ranked players high-ranked for a reason.
On the other hand, I don't think you should write people off simply because they have not reached a high-rank. I feel like a good admin is determined not only by his in-game skill, but also his interaction with players, maturity level, management and so on.
Let me tell you a good example - Raven never really was the most elite CS 1.6 player out there and although right now he's somewhat inactive as he's busy with his real life (although he will be coming back soon!) but I'd still take him over any high-skill cs 1.6 mixers, if the mixer is a jerk, I think a humble guy with will to improve and be fair with everybody would make much better admin than the high-skill player who'd however make a mockery out of the server.
I do think the rank of the player should be one of the factors when determining admin - but it should not be something to decide whether one will be admin or not - for the sake of a high-quality admin team - and unless a miracle happens and I'm somehow convinced otherwise, I refuse to let purely rank decide the application of our CS:GO applicants.