It is still definitely possible without the DK or druid. You just have to adjust you raid to work with it. The project marmot guides, specifically Ciderhelm's Sarth+3 will show you some techniques that can be used to help make it work. People like the DKs because they can use their own cooldown in succession first, and therefore not have to rely on other raid members for the first few breaths. They like druids because those melee swings really do a number on the tank, and having the avoidance/mitigation helps with healing.
By no means are they required, i have tanked sarth in all the positions with my guilds before.
Here are some of the movie links that might help.
[ame=http://www.youtube.com/watch?v=uRb7qV07ikU]YouTube - TankSpot's Guide to Sartharion 3 Drakes[/ame] -ciderhelm
[ame=http://www.youtube.com/watch?v=iJJ4hhL9DU0]YouTube - TankSpot's Guide to Sartharion 3 Drakes (Alternate Strategy)[/ame] -lore
Also if you search around in this same forum you can find some very handy information posted by some of the Tankspot users who lay out all the abilities that you see during the fight. Understanding those is one of the most important things you can do.
"If I'm doing a fight and I need more threat... I try harder. If I'm doing a fight and I need my taunts not to miss, then I wear hit." -Veneretio