Doesn't seem that many uke builders here use glue, but in guitar circles you'd be quite a rare breed not to.
Most will use something like Titebond on the tang before hammering or pressing in. I use Hot Hide Glue and this has been used for a very long time. Others will install the fret and then wick thin CA glue from each end. This method is good if you don't bind your fret board and have a tiny slot that needs filling. Wick in some CA. Let dry and then give the edge of the fret board a light sand. Don't blow out the dust from the fret tang slot. Put another drop of CA and it will harden up the sanding dust. Sand smooth once dry. On ebony you will not be able to see where the slot was. On there woods it may end up being almost as un-noticable.
It doesn't make the fret any more difficult to remove should the need arise. Not all that common on a uke to need a re-fret, but really common on a steel string guitar. Just a little heat from a soldering iron on the fret itself and the glue gets soft. Remove fret as you normally would.
What it does for the instrument is provide a rock solid seating to the fret. Gives better transfer of energy from the string. This may be less noticeable on a ukelele with such low tension on the strings, but quite evident on a steel string guitar.
This isn't going to miraculously turn an ordinary instrument into a killer one, but it's little things like this that all add up to take your building from ordinary to extraordinary.