Correct. You can add multiples to your uber account (not sure if it is "unlimited" but more than 5 can be added), but the codes do not stack. So the maximum discount per ride from these code would be $5 per ride.
Have:
$5 Uber promo codes good toward one ride, exp 5/15/19, does not work for Uber Eats
Want:
$1 Amazon per code
Also willing to trade five $5 Uber promo codes for one $4 Amazon GC