Shapes need to be transcribed in Nemeth, but the entire table does not need to be. Your code-switching decisions depend on what else is in the body of the table. If that square is the only Nemeth item in the table, just the shape symbol can be between Nemeth switch indicators and the rest of the table can be in UEB.
There will always be times when this just simply won't work. In such a case, you can use a different method as long as you explain it in a transcriber's note. This would be the exception, of course. If you can post an image of the print, I can give better advice.
Note that icons follow different rules. An icon can be transcribed in either code.