It's reasonable to conclude that this will be the case, but here's something else, from a different game, that proves that the DS is fully capable of reading a GBA cartridge while a DS cartridge is loaded and playing:
http://www.gamespot.com/ds/puzzle/jamwiththeband/news_6128617.html
http://www.gamespot.com/ds/puzzle/jamwiththeband/news_6128617.html