Probably not. In the default scheme of things, when you're connecting to both LAN and Wifi, LAN takes preference.
Code:
# netstat -rn | grep default
default 192.168.1.1 UGSc 25 0 en0
default 192.168.1.1 UGScI 0 0 en1
In the above, there is two default routes[1], one for each device. Routing tables are read from the top to the bottom, so packages will go out the first default interface. If that fails, it will go out the second. en0 is the wired, en1 is wireless (at least on my box).
[1] Actually, there's four, two more for IPv6, if you have it.