yes that is how it is supposed to work but it also depends on the order you cast them I think so if you cast 25% spirit blade then a 30% life blade on a 100pt attack it should look something like this...
100 x 125% = 125 125 x 130% = 162
so as long as the offending denizen doesn't have any resistance, weakness, or extra bonus on your clothing you would do around 162 points of damage