Yes, it is. HP-UX favors caching for performance versus large amounts of free memory. (If you have a PC/x86 background, you'll hear similar discussions about Vista RAM use). Until RAM is below a certain point (lotsfree -- see the Memory Management White Paper at:
http://docs.hp.com/en/1218/mem_mgt.html ), the system will allow objects and pages containing valid I/O data to remain regardless of size. Only when the system begins to come under memory pressure is this memory released for new allocations. In practice, this means that even an idle system can be sitting at 98 to 99% memory consumption if there was a prior kernel / I/O load causing the caches to fill up.
Free memory is not a good metric for if your load is stressing the box. What you don't want to see is Page Outs in Glance or vmstat [some is normal... but constant pi/po activity indicates paging is taking place and the memory pressure is impacting performance. Cache reclamation will not cause paging... the data in the caches is just discarded and the page is reused for new purposes].
