All the oracle processes are kicked off by the
oracle executable, and if you're running multiple databases on a server, all of the processes for each database will show up with just that executable.
args option to the
ps command will add the database name both for the instance processes (such as
pmon) and server processes (those satisfying user activity) to the
ps output to allow grepping.
What I don't know is what you'll get is useful, considering
ps is a snapshot of activity as of a given instant in time, and that seems like a very strange way to do capacity planning.