When importing into CiviMember, I would expect similar behavior as what happens in CiviCRM imports, especially since the interface is similar.
I've noticed two minor differences:
1) Validation testing before step 3: At step 3, CiviMember tells you the number of valid rows in the file. It doesn't look like CiviMember actually does the validation testing. (Though, I noticed, if I click the browser back button from step 4, I see the output that I would expect to see with the "rows with errors" count)
In my test file, Membership Type and some emails are not valid, and they make it through step 3 just fine.
2) The Import_Errors file: When CiviMember reports Import_Errors in a csv file, and the original csv file has column headers, the Import_Errors file does not increment the record number to account for the column header row. This makes it difficult to quickly find entries by the excel row number (although it may be more accurate, arguably). CiviCRM Import_Errors file does the increment in these situations.
You can see both of the above using my test file for individuals, with the saved matching fields called testbug2.