Comparing AmigaNet Hydra 500 and AmigaNet ZorroII, they seem to be the exactly same card, with the A500 model having Z2-to-500-expansion-slot adapter (it even reads "AMIGANET A500 CONNECTOR"). Makes sense, since it allowed reusing the design and components.
Whether it uses DMA or not, I have no clue, but I can't see why it couldn't. A500 expansion port is basically Z2 slot, and as far as I know it is cabable of DMA.
Compare:
AmigaNet Zorro II cardAmigaNet Hydra A500 insides
