The draw skill which is activated at the end of the turn can stack. This means that regardless of how many unit(s) is/are retired at the end of the turn, you will be able to draw cards up to the number of rear-guard attacks you made this turn.
Q: If I choose a Stamp Sea Otter using this unit's Limit Break, at the end of the turn, even though Stamp Sea Otter is unable to be retired due to his own effect, will I still draw a card?
A: Yes, you still draw a card. Because retiring a unit is not a condition for drawing a card, draw as many cards as this effect allows.