IOM does not behave any differently in Validate Mode than it does when you are not using Validate Mode. You will still get all of the interactive pop-up boxes and selection options when NOT in Validate Mode.
Validate Mode was intended for you to use to test a new file, a new profile, or a combination thereof, with just a small number of rows (25 or less is our recommendation). It was intended to be used to discover issues that would cause every row, or most rows, to become an exception. Example: Missing Constituent Codes on new records, a School ID that is incorrect, etc. It was not intended you would use this mode for all imports.
Validate Mode can, effectively, lock the entire RE database for all users that are NOT the user running the import in question. It isn't simply a matter of the tables being locked for some things for your users.
Please let me know if I can be of further assistance.