How do credo-baptists explain baptism in the Nicene Creed? How do credo-baptists explain "baptism for the remission of sins" in the Nicene Creed? Is this phrase interpreted in some way as being symbolic?
The Credo-baptists that affirm the Nicene creed, would argue that "baptism for the remission of sins" need not be interpreted as "baptism accomplishes the remission of sins", but more along the lines of "baptism witnesses the remission of sins" eg:


  ... The phrase, “We confess one baptism for the remission of sins,” does not mean that baptism leads to forgiveness of sins but that the Christian gospel depicted by baptism is the only gospel that truly saves. This creed was an appropriate response to false teaching of the past, and it remains a useful means to guard against false teaching that might occur in the future. - (Delray Baptist Church, Alexandria VA, "in friendly cooperation with the Southern Baptist Convention")


Further background information on varying Baptist responses to creeds can be found at  Baptist Theologian (Gardner-Webb University, NC) Stephen Harmon's post "Do real Baptists recite creeds?".