I had actually moved on HP cargo when I transfered to a field station, but that was pre 9/11. I am quite sure that cargo for employees is still not allowed (in the bulk I'm thinking of) due to 9/11 restrictions on cargo.
That being said, HP pass travel policy does not charge excess baggage to employees and their eligibles for items up to 99lbs.
From the horses mouth:
D. EXCESS BAGGAGE <
1. FEE WAIVED BAGGAGE <
NO CHARGES WILL BE INCURRED ON EXCESS BAGGAGE FOR
PASS TRAVELERS -EXCEPT UNACCOMPANIED GUEST PASS
PASSENGERS- AS A WAY TO LIMIT CARRY-ON ITEMS,
UP TO A MAXIMUM OF 100LBS PER PIECE CHECKED. THIS
INCLUDES SPORTING EQUIPMENT. HP DOES NOT ACCEPT BAGS
OVER 80 INCHES. FOR THE EXCESS BAGGAGE POLICY
PERTAINING TO GUEST PASS PASSENGERS, SEE G*97.
NON-REV PSGRS *ARE NOT* TO BE GIVEN SPECIAL HANDLING
TAGS EXCEPT FOR ACCEPTABLE ITEMS SUCH AS STROLLERS
CARSEATS, WHEELCHAIRS/ASSISTANCE DEVICES, AND
DEADHEAD CREW LUGGAGE.
However, just from my own experience checking in 18 boxes as checked baggage, you may want to arrive early, and if this is a station you work in, talk to an agt ahead of time so you dont end up on someone's bad side, haha!