Where do people get this idea that Vulcans are all pacifists? Was Spock a pacifist? Was Tuvok (a starship's chief of security
) a pacifist? Was Captain Solok from "Take Me Out to the Holosuite"? Was Sakonna from "The Maquis"? Was the Saratoga's captain?
Yes, Surak, as we saw him in "The Savage Curtain" was clearly a pacifist (and bear in mind that was Spock's perception
of Surak, not necessarily exactly who he was, as we saw with Kahless), but that doesn't mean the entire race is bound to dealing with an invasion force Ghandi-style.
(Oh, great, now I'm picturing Ghandi doing that viral video dance).
Seen as Surak was introduced (by Spock) as "The father of Vulcan philosophy", and in Star Trek Vulcan (as every other race) is a Planet of the Hats, http://tvtropes.org/pmwiki/pmwiki.php/Main/PlanetOfHats
it is safe to assume all Vulcans are pacifist.
That doesn't mean they would go all "Ghandi-Style"
and do nothing when the Romulans attacked. Spock was capable of violence, given no other logic options. (and in cases like spores, atavachrons, ponfarrs, etc
But they would absolutely not cooperate, and with billions of Vucans not acknowledging they were conquered, probably the 2000 Romulan soldiers would kill Vulcans until they got bored then die of frustration.