Yes they can but it will take a long for it to hatch:)
Can Ditto And Dialga Have A Egg?
YES! Because rotom and ditto had an egg and there gender is unkown
Yes but you have to cheat to make them breed then put ditto and dialga in the pokemon day care and use the cheat and there should be a egg then just walk and it will hatch it takes a lot longer then normal eggs to hatch though it will say "it looks like this egg will take a long time to hatch"but it should hatch into a dialga or any legend pokemon. Hope this helped
No but what a shame
No because I got a poketch an it showed if pokemon liked each other an they didn't like each other(Ditto and Dialga)
NO! BECAUSE DIALGA'S GENDER IS UNKNOWN