Yes, democratic peace is used as a pretext for war, because politicians often use the goal of spreading democratic peace when making their case for war. Politicians say that if only these nations are given the chance, they will embrace democracy and their nations will flourish. This is what many politicians, particularly Dick Cheney, want when they go to war.
No. The democratic peace theory is the hypothesis that democratic governments will be passive when disagreeing. I do not believe this theory is a pretext to war, since supporters of this outlook encourage the theory's premise that there should be an unwritten understanding between democratic governments that disputes can be settled at the table, and not on the battlefield.