This is one of the unfortunate side effect of us not really being able to depend on JDK in a proper packaged way. Currently the hadoop package quite rightfully depends on libjvm.so but the trouble is that Sun/Oracle JDK RPM package doesn't really "provide" libjvm.so from RPM/YUM perspective (Sun/Oracle JDK RPM package in general cuts a lot of corners in packaging – that's just one of them).
What this leads to is that YUM keeps looking for packages that DO provide libjvm.so and in some cases the only one is libgcj. Thus the end result is for a user to see weird dependency on libgcj when installing hadoop package. It should be noted that this is harmless. The right libjvm.so (from Sun/Oracle JDK) is used during execution and libgcj is just quietly sitting there.
As a side note, in a true enterprise case (RHEL) the right thing happens – a properly packaged JDK from RHEL channel gets pulled.
Now, it would be nice if RPM has an option of disabling just THAT one auto dependency (on libjvm.so) but I'm not aware of such a thing. Hence this fix disables ALL of our automatic dependencies.