1 of all – no you cannot install any plugins on your Ilive.
You can use either the M-Waves Card along with an Waves Soundgrid Server or any Host with Plugins along with the Madi Card.
Take a look on the thread of “Mumu” what he writes about his experiance with Dante.
The “normal” Dante Card is not recommended (in my opinion) for use with Plugins cause the latency is too much.
I would suggest – get a look on A&Hs Youtube Page – there is an Soundgrid Tutourial – or have a look on http://www.waveslive.com
The second question: yes its possible, but is that necessery? in smaller venues insert an multiband compressor does not work for me very well – because the Mics getting far more sensitive for feedbacks. At least for me.
I am running the M-Waves Card along with an Soundgrid Server and Waves Plugins. (For now only Waves PlugIns are supported, but Waves opened Soundgrid to 3rd Party Plugins now – so more should be coming).
Hope to help you a little.