Can flexbox divide items evenly on multiple rows?

No, not without media queries adjusting the flex-basis value. Flex items that stretch and wrap attempt to maximize the amount of items that fit on each row.

You may want to consider using the multi-column module instead, which will attempt to equally distribute elements across all of the columns created:

.foo {
    columns: 100px;
}

http://caniuse.com/#feat=multicolumn