My rotary Mazda has an oil injection pump to keep the apex seals lubed, but that's a horse of a differant color.
If you look at the geometry of a cylinder head you will see where oil injection isn't such a good idea- you don't really want oil on the valve seats because they will ash and not seal well. A properly designed valve stem seal leaks just enough to lube the guide. Exhaust valve guides tend to wear due to ash on the stems- and oil consumption causes ash.
When was the last time you had valve guides fail before something else was worn out on an engine?
