After 6 hours of trying to send a print job from a Mac to a Dymo label printer attached to a Linux computer, the solution was to not use the Dymo printer drivers, but simply the "Generic printer" drivers. Works like a charm.
@cgiffard Absolutely. We have a box of prototypes, we'll take some progression pics and I'll write up the steps these thingies go through. It's not as easy as one would think. (Which I did, until we tried)