My ds is Amos - I love it. To me the pronunciation is not very like anus at all. Nobody has ever called ds anus, but he is not starting school until September, it certainly wouldn't occur to me. I am confident it wont be a problem. Kids can make any old nonsense out of any name.
Amos is not any closer to Anus than Will is to Willy or Benedict to Bendy Dick or Ellie to Smellie Ellie or any other name to any other silly word.... In other words kids will tease any name. But in my experience kids actually accept most names for what they are - there doesn't seem to be much teasing about names at my dcs school (and there is a big range of names from all cultures!).