what does an EGR plate do?

Depends on what you are calling an EGR plate.

If you are reffering to the EGR spacer that goes between the TB and upper intake, then it mounts the EGR valve, flows coolant to keep the egr and intake charge a little cooler. and gives you a place to mount your throttle linkage and TV cable (AOD only)

There are also small plates that bolt to the opening where the EGR valve is mounted to the EGR spacer to bypass it. (not a good idea unless you block the egr at the head also). Or a thin metal spacer that replaces the entire EGR spacer, elminiating the EGR function and spacer but leaving you a place to bolt your throttle linkage and TV cable.
 
Will this work with AOD?

Does this one look like it will work with an AOD? I was going to get the BBK TB and spacer/plate and bolt it to a ported stock intake.
 
Yes it will work, I just threw in the AOD part for the TV cable, its really not a factor in choosing a TB/EGR spacer.

If you go with that, get a 65mm TB to match it and if you are putting this on a stockl intake, you will prolly need to do some grinding on the intake openining to match it. If you are putting it on an aftermarket intake, most are opened up for a 70mm.