I don't think this will be a problem. A classic gas laser can have variations of more than 1 wavelength in its cavity without any issues. I believe this was one reason for the relatively short coherence length of HeNe lasers, but I could be wrong.
I bet you the lasers in these transmitting devices will not be gas but small solid state units. As this becomes more popular, like surface-mount camera dies, these SMD IR laser diodes will become smaller and smaller.
They are probably using semiconductor units (with lasers "solid-state" usually refers to non-semiconductor solid lasers, such as ruby lasers). My point with HeNe lasers was that having variations in the cavity length is not a problem for lasing.