You can't run the SIM files, you just select a game with the proper extension (like .nes for the NES) an the OS knows what SIM file to use. Every SIM emulator is associated with a file extension and you have to be sure not to put two emulators associated with the same file extension on your Dingoo.
The emulators you can run are APP files, and those let you select any file and probably support zipped and unzipped files.
OpenDingux is updated, but some people still use legacy dingux for some emulators. You don't "have" to change to OpenDingux unless you want updates and bug fixes, Legacy Dingux is deprecated and most of the new emulators won't work on it.
Also, you're probably not setting the emulators in the right way, search here how to use the "file browser" option of GMenu2X. Few emulators have a file selection menu, the rest expect you to chose the game using GMenu2X and if you just open them they close because they don't know what game you want.