I assume the two confounding factors are (a) the satellite should be moving relative to the ISS at the speed it was launched, so it is going to take a while to come back around and (b) when it does come back around, it should only be going as fast as you launched it, so it shouldn't be nearly as dangerous as the typical orbital collision.
[Huh, if the cubesats are launched at 90 mph from the ISS (the speed of a fastball), it only takes ~12 days for them to come back around; that's quite a bit faster than I would have guessed, but still probably long enough for orbital decay and ISS adjustments to put them out of line.]
[Huh, if the cubesats are launched at 90 mph from the ISS (the speed of a fastball), it only takes ~12 days for them to come back around; that's quite a bit faster than I would have guessed, but still probably long enough for orbital decay and ISS adjustments to put them out of line.]