One of the most important parts of any computing project is to know how to enable your logfiles, where those logfiles exist and to read them diligently.
I don't think I would ask the question "where are my logfiles?" to others ---- I would think it is very basic to find, manage and read the logfiles myself.
This is the very basic part for anyone working on a computer.
Correct, if you wish to use OVM to manage your Oracle virtual machines you need agent on running on those hosts.
I haven't used those, but the logic is the same as with any other similar software.
Install agent on machine, establish communication to your central management server(s) (hopefully a secure one), and click away your virtual machines in your browser/application.
You should really care about security, since this exposes bare metal to https or similar protocols.
Also OVM uses application server (weblogic) and mysql enterprise database from Oracle.
It will introduce additional overhead to maintain and handle those, with a price list probably (this is just a guess).
Otherwise, you do not need agent and work is being done from command line.
Yes. OVM Manager is an optional component with OVM for SPARC. It is only required with OVM for x86 and is part of this product. The SPARC control, i/o and logical domains do not require or make use of this agent.