I know it's the Canon Corner and all, BUT...
I use a Substrobe MS all the time with (Nikon) housed DSLRs. Strobes in manual.
No need for an external slave trigger, the internal slave sensor works fine as long as it can see the strobe tube of the primary (wired) strobe.
If you are refering to housed digicams, generally the MS is inadequate; it dumps a full-power shot when triggered. Modern digital-compatable strobes, like the DS50, can watch the digicam's strobe output, and quench the slave's strobe pulse at the same time as the camera's, thus providing auto exposure. They also can clone the pre-flash pulses.
Manual? Go for it; my MS's have been incrediblely bulletproof. Otherwise, you'll need a modern strobe.
< ducks for cover and retreats to Nikon Niche >
All the best, James