You can oil both the nailers and the wrenches at the tool end of the hose.
However, the wrenchs, and chisels will need to be oiled more often. I
ususally put a few drops in the nailer every time I hook it up and let it go
at that. If the wrenches are getting continuous use, I stop every hour or
so and 5-6 drops.
As far as oilers go, they are fine and save a little time. BUT don't install
one at the compressor end. Keep it at the tool end or you will end up with
an air hose full of oil that will be there forever and all over you wood
projects. Some folks, who plumb air into their shops, put a dedicated
outlet with oiler, filter, regulator just for air tools. This is overkill
if you use the tools occasionally - Just put the oiler at the work end of
the hose with a shorter hose or coil hose to the wrenches.