It's not something I would go out looking to do, but if a slow moving vehicle happened to be in the right place and presented it self just in front of me, it would be hard to refuse.
In the time trial world, there used to be a few courses (E72) and probably there still is, that were notorious for their high volumes of traffic and the drafting effect of lorries gave some artificially fast times - sometimes 5 mins faster than you would do on a normal course. By drafting, I don't mean moving into the slipstream of a vehicle, just the effects of the vehicle overtaking.
Safe cycling
Keith