I noticed today that when I install dolphin, there is an additional executable dolphin-emu-nogui. This executable allows for me to launch it via the command line without the above error; however the "exit" key bindings are ignored when using this executable.
Update: Compiled from source from the latest commits in master (bf8ffe5bfb50ce1d2aa969ea6cc1901dc79a85ec), the dolphin-emu and dolphin-emu-qt2 are both working correctly. I do not know if this was an issue with the build that the unofficial PPA hosts, or if it was a regression that was recently fixed, but it does work from the command line now.
The problem with dolphin-emu-nogui still exists though.
Update: Compiled from source from the latest commits in master (bf8ffe5bfb50ce1d2aa969ea6cc1901dc79a85ec), the dolphin-emu and dolphin-emu-qt2 are both working correctly. I do not know if this was an issue with the build that the unofficial PPA hosts, or if it was a regression that was recently fixed, but it does work from the command line now.
The problem with dolphin-emu-nogui still exists though.