You can clear trash with less than a full raid, the only time meters that matter are on boss fights. Some are pretty unfrieldly to certain classes. On Prince, I get destroyed if I get a lot of enfeebles (I *always* run to max range and then some to avoid being one shot), but I do practically 40% of the raids damage on Maiden.

Honestly, look for trends over time and encounters. It'll be easier when you hit 25man content as you can judge people against their peers and not different classes. When you have 3 rogues and 1 doesn't even do half the damage as the other 2, you know something is amiss. Usually it's pvp spec issues, something your guild will have to address if it's currently "casual friendly" and you wish to make progress in future raid content. Like it or not, DPS is extremely important in currrent end game content. More so than ever before, including AQ40 and Naxx. We personally had Patchwerk kills where 2-3 of our key DPS classes died from Hateful Strikes in the first 45 seconds of the encounter. You won't see any such leeway anymore.

Also, listen carefully to peole who talk about alternate roles. For example, a key part of our Magtheridon strategy is killing 2 adds in the beginning with Rogues using Adrenaline Rush + Bladeflurry (HI 4000 dps!). But if you have melee on click duty they quickly fall behind. Click duty on this fight is the whole challenge of phase 2, it has almost nothing to do with dps, unlike phase 1.

So.. honestly, you just need to use common sense. While it may be hard to tell in a 10man when you are likely to only have 1 of many classes and have no realistic benchmark, over time it should become clear who your star players are. They will consistently do more damage than others, stay alive longer, come prepare, show up on time, and have feedback about strategy/tactics on progression content. Don't limit yourself strictly to DPS meters, it's just a data point.