It's quite a leap to conclude that just because he was playing BM that he was playing a spec not of the greatest benefit to the guild. There are many dimensions to the question of what most benefits a guild. Raw DPS numbers are but one single dimension and not necessarily the most important one. Yes, I know the primary job of damage dealers is to inflict damage, but it's not their only job. Concentrating on raw DPS is a terribly simplistic way of looking at what a character who neither tanks nor heals brings to the table. It's awful that we've dumbed down an entire broad category of characters to this single number.

When it comes to raid progression, the ultimate measure is not who did how much damage, but who contributed in any way to downing a boss. For example, in the case of a BM hunter, did he ever use his pet handling skills to pull a mob off a healer or a lightly armored fellow damage-dealer, making it easier for them to do their jobs? If so, he contributed in a way that will never be measured on any DPS meter, at least not to give him credit. You could call out an endless number of ways in which players contribute to downing a boss that are not easily measured by any addon looking at the combat log.

We need to get away from this simplistic min-maxing way of thinking, the notion that there is only one right spec for any given class just because some theoretical number says so. Your class, spec, gear, gems, enchants, all of those things serve to determine only your potential for succeeding in an encounter. How well you actually do has more to do with your skill as a player, things like how well you really know your class, your situational awareness, ability to adapt and improvise, and how willing you are to be a true TEAM player rather than a greedy glory hound. I've seen many a player with supposedly inferior specs and/or gear outplay those that some numbers say ought to be better.

Let's also not overlook the numerous intangible ways a player benefits a guild. Some people are more fun to raid with, even if you wipe, than others are even when you win. These people can help attract and retain other players merely by their presence in a guild. They can also motivate people to show up, on time and prepared. They may be generous with their professions, bringing benefit to other players with gear, consumables, and buffs. They may help others prepare for raid night with valuable information. I'll take a player like this over an asshat with higher DPS any day.