It also depends on the flash itself whether it has a fast recycling time or not.
I have experienced this before with so-so flashes when I was shooting Nikon SLR's then..when i used the SB speedlights, those things where fast, moreso if you don't output full power.
You can hit those with your motordrive and it will fire to sync with it.
Come to think of it, I remember those flashes to have a switch for a setting for motordrive wherein it doesn't fire full power and is fast enough to cycle in sync with the motordrive speed.