I have the Tokina 90mm f/2.5 with the 1:1 adapter, and have the exact same question as you do. I believe the Tokina is a twin of the Vivitar (not exactly the same, but close).
Here's why I think the Vivitar/Tokina 90mm Macro cannot be used on the Olympus bellows, though I don't have the bellows equipment to be sure. I believe the camera attaches to the bellows at one end, and the lens attaches to the other end of the bellows. Then, a double-cable release fires the camera and the lens diaghram at the same time. Obiously, the whole bellows mechanism is going to be in the way, since the 90mm lens attaches directly to the camera. The 1:1 adapter has glass elements, so cannot be properly replaced with just a bellows extension.
You can probably rig up a mechanism to hold the Olympus slide holder part of the set-up, but I have a feeling you can make a home-made slide holder fairly easily with a few trips to the hardware store (I can never make just one trip, it seems like).
The critical part is the distance from the camera to the slide. Too far away, you get too wide of a view, and too close, you don't get all of the photograph. So some sort of mechanism to exactly place the camera at the right distance is needed. Plus, when you re-focus the lens, the field-of-view changes (if even just slightly), so then you have to reset the distance between the slide and the camera (again, maybe just slightly).
But, it seems to me, after you have that all set up and working, duplicating slides should go very quickly.
I would recommend the lens front be shielded from stray light sources to cut down on flare. I almost got rid of the Tokina because it gets terrible flare. Then I read how good the lens was, and used it where it wouldn't flare, and it is a very nice lens indeed.
One other option, of course, is to get a Olympus 80mm Macro lens, which is also a very fine lens, and is known to work for this application.
Whatever you do, please let us know how it turns out. I have several rolls of Velvia 50 in the freezer, and a processed one down at the lab right now.