exactly how you said: load the sounds into individual slots in ultrabeat, use a multi output version, send each part to it's own output, and add whatever effects you want after that.
Easy...
Literally: Open a multi version of Ultrabeat. It has a + sign at the lower right hand part of the fader. Each time to press on it you get another aux output.
Once you have opened Ultrabeat, select the 1st oscillator (actually the second... the one on the lower left hand side of the selected sound) and add audio file... you might be able to drag and drop you audio file into the slot, but Logic isn't open right now for me to verify this.
Once you have the sound you want, and you have added some extra aux outs by pressing on the + key, go to the output selector (just to the right of the little pan pot after the part name) and change it from 1-2 to 3-4 or whatever out you want to use.
You should now have the sound you want going to an output that you can process with whatever effects you want to.
Like I said... easy ;-)