It's probably due to the fact that the GBA Dingoo Emulator isn't as advanced (no pun intended) as some others and is missing a file or part or something to make NES emulation in a regular GBA game work properly.
I would get the Classic NES Series Metroid Rom (can't provide a link) and make sure to patch it with these files: (legal, just makes the rom work) http://www.megaupload.com/?d=NS5J1PAK
That's only if you really want to play the version with the squished in sprites. Otherwise, why not just get the original Metroid NES Rom and play it with your native NES emulator? (Again, can't provide link) The native NES emulator is quite good from what I hear. Unless that doesn't work or you don't like it as much or something, then just stick with choice A.
(NOTICE: THE FILES I HAVE LINKED TO ARE PERFECTLY LEGAL. THEY ARE SIMPLY PATCHES TO MAKE ROMS WORK, BUT CANNOT BE PLAYED ALONE OR AS IS, THEY ARE SIMPLY PATCHES, AND ARE JUST AS LEGAL AS ANY TRANSLATION PATCH, THEY ARE NOT ROMS AT ALL AND I HAVE NOT PROVIDED A LINK TO ANYTHING ILLEGAL.)