I've heard this before. Personally I'd be nervous as fu...dge powering up a Miggy with one of it's custom chips missing, LOL. I know to use the Indivision in an A600 you plug it into a card in the memory expansion port (no Denise needed), but then the A600 already has a Denise on the motherboard. I dunno, would like to see a picture of someone using it without the Denise before I'd try it myself! 
Been there, done that
Powered it up with just the Indy installed and the Kickstart screen agreeably popped up just fine.
It isn't a case of "powering it up with a custom chip missing" anyway, as the Indy is a Denise replacement, registers and all. So as I see it, it just needs to sit somewhere with access to the CHIP memory bus, the RGA lines and a colour clock.
For example, on the A500 trapdoor connector, the RGA lines are missing, so it wouldn't be possible to install the Indy there without additional wiring. On the A600 trapdoor the RGA lines are there, so it can happily work there. Similar story with the A1000 where the Indy is installed alongside Paula via an adapter - the lines needed are there.
There's only one possible gray area here - mouse movement. Denise has inputs for the mouse movement pulses and these are of course not routed to either the A600 trapdoor or Paula. So it's obvious that in the A1000 and A600 case the Indy does rely on the actual Denise being present, to count mouse pulses.
On the A500/A2000/A3000 case it sits on the Denise socket and therefore has access to the mouse inputs, whether it implements pulse counting in this case or still relies on Denise I can't remember. I'm unsure if I booted my A500 beyond the Kickstart screen when I tested the Indy without the Denise, it's been 2+ years since and have no real desire to take that A500 apart again!
But rest assured that powering it up without the Denise is harmless, so if you feel like trying it out you can fill in my lack of memory for the possible mouse issue
Happy holidays!
