It doesn't use Denise for the A600 (it does for the 500/2000, from what I've heard - won't boot without them installed), but it still has to be getting the video signal data in the A600 from somewhere, right? And the only way it could know what pixels to put where is going to have to be coming through the trapdoor slot...
The IndyECS does not "use" a Denise in any system.
You still need an Denise somewhere.
The IndyECS also does not use any video-signal coming from Denise (in contrast to the AGA-Indies and Lisa), what it does is react on anything happeinng at the chip-mem/set in the same way as Denise would.
This data is then used to generate a VGA video-signal.
