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.
So, what about an arrow? In Nemeth, it begins with the shape indicator, so would it also need to be Nemeth or a tactile? I am sending an example of one along with the boxes. I see arrows in regular text simply meaning next step but could not find an example at the moment of this type.
You are right that the arrows in your sample are not math arrows. They are lead lines or pointing arrows. I believe tactile graphics would say that the arrowheads be omitted and that the lines not be at a diagonal angle. I suggest you post this question on the tactile graphics forum and see what they recommend.