You can't hide the empty arrows and why would you want to? They need to be accessible so that if you accidentally remove an object from the tab order, you can put it back in the tab order at a later time. I suppose FileMaker could add a feature to hide/reveal the empty arrows, but this is not a feature that exists at this time.
There are times when layout objects are small and/or overlap one another where the arrows get in the way of each other though I don't see any such problems in your current screen shot. In those cases, it can be a bit of a hassle to edit the tab order. I've had to move the layout objects to more widely spaced positions after first writing down their position as shown on the position tab, then edit the tab order, then refer to my notes to edit the top, and left boxes in the position tab to return them to their original location.
It is a problem, zooming in or out does not change the relative sizes.
FMP Help Page for Set Tab Order http://www.filemaker.com/help/html/edit_layout.10.30.html
Tab Order And Field Behavior Explored
How do I change the tab order of objects on my layout?
The size of the arrows is a particular problem. @philmodjunk - suggestion of moving layout objects around seems to be the only way to deal with the problem when you have overlapping arrows - but that is less than ideal.
Here's what I do. In layout mode highlight the fields you want in your tab order to group them. Invoke the Group command. Note the Top and Left position of the grouped object. Copy the group and paste it to the side of your visible layout (outside your bounds). Clear the tab order then in the pasted object set your tab order. Delete the original grouped object then set the position of your pasted group to the top and left position and ungroup (or not) then save the layout. Tab order should be set.
Phil's solution is the same I guess. I haven't tried this with fields that have object names. Going to try that right now.
[Tried it - objects get an appended number so you would have to delete them from each field that might have it.]
After some frustration I've found that I can usually sort out overlapping arrows without moving fields etc if I zoom to 400% and then the arrows are almost always slightly offset enough to allow you to select separately.