Can an iMac connected via Ethernet to an AirPort Extreme participate in the Wireless network? I have a home network made up of an AirPort Extreme and an AirPort Express that is set to extend the network.

Currently, my iMac is connected wirelessly but I have the option to connect it via Ethernet which I would like to try out.

My question is this: a number of features in iOS and OS X take advantage of the local wireless network (e.g., sending green bubble messages from the Mac through the phone, streaming audio through something like Airfoil, printing to a WiFi-aware printer). 

If I connect my iMac with a wired connection to the AirPort Extreme, will it still be able to participate in the local wireless action? 

If not, can I connect it through Ethernet for Internet access but leave the WiFi on just for the local stuff?
Actually you may have a minor, if understandable, misunderstanding of how a network works.

If you plug a Mac (or a PC, or anything else...) into a base station that other computers connect to wirelessly they are all on the same network.

Neither MacOS nor Windows, Linux or anything else differentiates a wireless network with a wired network coming from the same source.

Try it out, turn WiFi off on on your Mac and then try those things out, you will find that they still work just fine.

Note that the "green bubble messages" distinguish a text message (or SMS if you prefer) that goes over only your carrier's cellular network from the "blue bubble messages" (iMessage) which use your phone's 3G or 4G networking to send data through Apple's messaging servers. This is why your blue bubble messages never get to anyone who don't have an iPhone or a Mac.