The grep really isn’t necessary, you know…

awk can apply rules to lines based on lots of logic, for example a regular expression:

svn st | awk ‘/?/ {print “svn add “$2 }’| bash

Which would only act on lines that contained a question mark. Of course you could change the pattern to be more exact using:
/^?/

And if SVN didn’t use a question mark for that status, you wouldn’t need the backslash, but I didn’t invent the thing.