The 6800 series was second-sourced by several manufacturers and should basically be plug compatible if the application circuit was designed in accordance with the original Motorola datasheet. There may be subtle differences in the chips between different manufacturers but these shouldn't affect normal operation of the chip.
Where you might run into trouble is when the designer has used some undocumented feature in the chip or pushes it past the datasheet specifications or selects the chip for specific performance parameters. In this case you can expect some second-source chips might not work as intended. This is unlikely to the case if you are looking at HP designed equipment.
The 6800 family was produced as a true second source by several manufacturers, which you can rely on as being truly equivalent.
I spent a good deal of my first year as an electronics engineer debugging troublesome 6800 systems and I found that there were subtle differences on how second source chips from different manufacturers behaved. The 6800 system was initially developed using Motorola parts and all seemed fine. But when production transferred to cheaper AMI second-source parts there were a lot of random field failures. As it turned out in the final analysis it was the support circuitry around the 6800 that wasn't up to scratch and not the processors themselves.
Nevertheless the different brands behaved differently with the dodgy support circuit. This may have been down to manufacturing process variations or it may have been that AMI slightly relaxed their test specifications to get a better production yield and a lower chip price.
This includes at least Philips, Thomson (ST), and Hitachi. However, I don't think Mitsubishi made 6800 family parts.
I don't recall Philips second-sourcing the 6800. They did second source the 68000 and a number of 68000 peripheral chips.