I guess it all depends on how accurate a reading you are comfortable with.
Even using a test jar pressed to the end of my nose, I still have to do a lot of squinting to come up with a reading.
Not to mention a bucket fermenter, I've never tried to take a reading through the class/plastic wall of a carboy because I know that it will be even more difficult than using a test jar.
With a bucket fermenter, I imagine that I'd have to stick my head down into the must to get an accurate, eye level, reading, but I would still wouldn't have much confidence with such a reading, because I would have to be reading it upside down!
If I'm going to be working with ballpark readings, I'll just throw the hydrometer away and really ballpark everything.
Besides, taste testing the sample is an important test, too...to me, anyway!
Pogo