Yes, someone can be considered multi-religious. In fact, there is a word for someone who recognizes and respects all religions. The word is omnist. An omnist can also “accept the existence of various religion without believing in all that they profess to teach”. I agree with a comment in a recent study by PRRI (the Public Religion Research Institute) which “found that sixteen percent of Americans currently say they follow the teaching or practices of more than one religion”.
Another study by PRRI concluded, “While there has been little research done on this question, the increase of religious diversity and interfaith marriages make it likely that more Americans may follow the practices and teachings of more than one religion.”