select queries on data-only-locked tables do not block on uncommitted insertions when the following conditions are true:
The table uses datarow locking, and
The isolation level is 1 or 2.
Under these conditions, scans skip such a row.
The only exception to this rule is if the transaction performing the uncommitted insert was overwriting an uncommitted delete of the same row done earlier by the same transaction. In this case, scans block on the uncommitted inserted row.
