Net 2 and EOS

Yes, this is correct. Starting with software version 3.2 Eos does not support the ETCNet2 protocol anymore. This is also true for the protocol AVAB-UDP as well as the draft version of sACN.

In this support article you can find an overview of which software and hardware version support or don't support ETCNet2.

Thank you.

To update ETCNet 2 to ETSNet3 do I need to replace the infrastructure cabling also? Or data cable that is been used for ETCNet 2 will work for ETCNet 3 also? What about the dimmer racks? At this moment the venue is using ETC CEM+ dimmers, is it ok to use ETCNet 3 with CEM+ ? 

Net2 was a network protocol, Net3 is one as well. The cabling in general should still work, depending on the age of your installation you might want to look into replacing your cabling in the next year's, but that is independent of this change.

CEM+ understands both Net2 and sACN (which is part of Net3). So you can still work with your CEM+, it might need a firmware update.

Are the dimmer racks the only networked receiver, or are there maybe house light control panels or Net2 gateways to convert network to DMX?

yes there is house light control panels and Net2 gateways.