Well, it's good style NOT to ignore those error messages, especially if you're making a level for Lemmix, as maybe some players are playing their levels in DosBox/CustLemm, e.g. if you don't have Lemmix because you're running on Linux. The errors are exactly what the error messages say: the x coordinates of those objects (traps, hatches, water, etc) are not divisible by 8, which would make the level not run in DOS lemmings.
Though to be honest, by now I think it's unlikely that anybody will play your levels in DOS Lemmings/CustLemm, so it's not a big issue to ignore them.