Sorry, the heap viewer has not received the love it needs of late. I don't think anything significant has changed from 1.4 to 1.5, so the viewer should still work. Just a change from 1.4 to 1.5 in the header.
The heap dump viewer should work on pure Go dumps. I've received problem reports on Go/cgo mixed applications due to unparseable (by the simple dwarf reader in the code) dwarf entries. I'd appreciate patches if you have the time to look into the failures.