Germanic loans in Proto-Samic

For future reference: *a > *ō in Proto-Samic was later than *ē > *ā in North Germanic, so any PS entry that has *ā in correspondence to a Germanic *a (or *ā), as in e.g. *mānō, is better marked as a loan from Proto-Norse than Proto-Germanic.

(I guess it would be also possible to add Northwest Germanic as a "PG dialect", similar to what we do with Proto-Uralic vs. Proto-Finno-Ugric, but this doesn't seem like a move that would have terribly numerous benefits.)

Could the word not have been borrowed with Germanic ē being substituted by Pre-Samic ǟ?

That much is possible in principle, yes, at least in the case of roots of the shape *ā-ē < *ǟ-ā, though anything that early can be usually told apart by other signs (e.g. by Finnic equivalents that have *ä).