@dre0017,
Sure I believe. Additionally, it would seem to me that some of them may be living among us.
How did they get here? On spacerafts which are undetectable to our current technology. Further, if they were/are able to travel these grew distances in a relatively short period of time, they might only be seen as a blip on a radar, if noticed at all, due to their speed. Once here, they either are able to change appearance and thus assimilate or they already have similar appearance to Earthlings. It that advanced, learning local language will be a breeze.