I believe they do, but I can't track it down in 30 seconds or less. Belichick was an assistant at New England from like 96-97, and Bo was an assistant there from 97-99, and then Bo left when Belichick took over for good in 1999.
Someone with more knowledge or time will have to figure out if they coached together somewhere. I want to say they did, but I can't recall.
From a quick wikipedia search, Bo was at New England from 97-99 which is when Belichick was at the Jets, but they may have crossed paths when Belichick was at New England in 1996 before he left for New York.