Put the video card in master and what ever other card you have in slave. Shouldn't really matter though I've found.

I think the master slots are for the cards that do bus mastering. I posted the same question on this forum a while back and was told that there are no VLB video cards that take advantage of it, so it would be better to save the master slots for controllers or other cards that may be able to use it.

Regarding how to identify the VL MASTER/SLAVE slots, it's usually either in the manual or silk-screened on the board. I'm not aware of any other way to determine that.

Master/slave nomenclature is somewhat unclear on VLB. But indeed, I believe that master slots allow cards to be 'bus master'. This means that the card will initiate a bus transfer, instead of the CPU.
A regular SVGA video card will never do this, all bus transfers are initiated by the CPU, and no DMA is supported.

There might be certain advanced disk controllers that may use bus mastering on VLB, but not your standard EIDE multi-IO cards. If they exist at all, they would be advanced caching controllers, possibly SCSI ones, which have an onboard DMA controller that initiates bus transfers.

Perhaps video capturing cards may also use bus mastering, or advanced network cards or such.
But not standard SVGA video cards, at least.