Dumps made with dump-0.4b11 on Alpha are not readable on x86. This issue is resolved in the most recent version, which at this time is dump-0.4b13. In conversations with the maintainer, Stelian Pop <pop>, it appears the issue is with time_t and its use in the dump header.
Yes, time_t issues on alpha have broken cpio and rpm to name but two. I've just compiled dump-0.4b13-1 in Raw Hide.