7-Mode is still 7-Mode, so yes, the any NSO-154 study materials would still be very usefull for taking NSO-155.
You may wish to review the certification web page at: http://www.netapp.com/us/services-support/university/certification.aspx
I'd advise that you read through the Data ONTAP 8.0, 8.1, and 8.2 7-Mode Release notes.
There are many web based trainings (WBT) available on the Learning Center you may want to take advantage of as well.
Of course, we'd always love to see you show up in class for an instructor led training (ILT) D7ADM class !
I hope this response has been helpful to you.
At your service,
Eugene E. Kashpureff, Sr.
Independent NetApp Consultant, K&H Research http://www.linkedin.com/in/eugenekashpureff
Senior NetApp Instructor, IT Learning Solutions http://sg.itls.asia/netapp
(P.S. I appreciate 'kudos' on any posts.)