Since Dada-Alias fails to compile with perl 5.12.1 (which is in the perl-experimental overlay), this dependancy makes Data-Visitor "impossible" to merge. This dependancy is not required for normal work with Data-Visitor, and on CPAN it's actually commented out as you can see here: http://cpansearch.perl.org/src/FLORA/Data-Visitor-0.27/Makefile.PL We should probably follow CPAN and comment that out as well, which would also make everything work with perl 5.12.1.
I think it's a dupe of bug 314933 See also the discussion in the URL of that bug. I've seen the comment in Makefile.PL but Data-Visitor fails its tests without Data-Alias. *** This bug has been marked as a duplicate of bug 314933 ***