I wouldn't make the buttons end grain. Buttons are quite thin and will be very inclined to chip and break around the edges in use if made that way around.
I have some old wooden buttons myself - they all look as though they are made of beech and most are still heavily varnished (although on some the varnish is now crazed with age). They are all long grain. Most came from coats or heavy wool cardigans that were rarely washed and if so, washed carefully by hand in cool water. Some have holes in (2 or 4) others have a metal loop on the back. The holes do not seem to have suffered from any splitting or cracking.
I also have some wooden toggle-type things on some modern clothing that get frequently machine washes. The toogles look like they were made of beech and were lightly varnished when new. After a few washes they are still functional, no splts round where the hole is, the varnish has disappeared and the surface of the wood is rough - like a used wooden spoon. To be honest, the wooden toggles have lasted longer than the thread (or quality of sewing) used to attach them!!!
tekno.mage