If you manage this host, I'm a little concerned you're asking that question here
Like mentioned above, mpxio is a multipathing solution provided by Sun. I prefer it, I think it's a clean implementation and easy to use. And free!
Unless you're limiting what you want to enable with mpxio, you don't need to modify any files, running `stmsboot -e` will do that for you.
Why are you talking to Sun, and why are they suggesting this? Are you having trouble getting DMP to work properly with your EMC storage?
Giving us some versions of veritas, your HBAs and what storage you have would help. Depending on those answers, you may need to install additional array support libraries and adjust the failover mode on the storage itself (if you're having DMP trouble).
Enabling mpxio will consolidate all of your device paths to a single "virtual" path per unique device. Normally if you have 5 LUNs with 4 paths each, format for example would show 20 devices. With mpxio, it'll only show 5.
If you enable mpxio without taking care to do it safely on an already running system, you could be in for a world of hurt. I've seen odd issues when enabling mpxio, with emc attached storage, on an already configured host with veritas. Changing a 10 minute maintenance into a few hours.
Good luck.