I am also an HPUX admin. It sounds to me like you know what you are doing.
Anytime you can gain additional knowledge regarding UNIX I would take it. I started out with no degree and recieved my AAS degree in UNIX. I have taken a separate Unix Cert course at the local Junior College.
It sounds like this is a very good course and Linux is becoming more popular. All the next versions of the Cell-based Superdomes and Keystones from HP will fully support LINUX OS.
You have the right attitude regarding CERTs. They are nice to have but I wouldn't rely on them getting you a job or promotion. However, for 2 people with the SAME experience, that might tip the scales in your favor.