Hi gardelove,
The Moonvine(Ipomoea alba) can be grown together with day flowering MG's and they will not cross fertilize.
You may also like to try the Moonvine Ipomoea macrorhiza as it also produces a nice large flower as compared to the nice lavender colored,but relatively small flowerd Ipomoea turbinata.
You didn't mention what climate zone you are in,so I can only speculate as to whether the plants would have enough time to produce mature seeds,but starting them early can be helpful.
The moonvines will usually not successfully replant themselves from seed,because the colder climates have repeat freezes and re-thaws that the seeds will not survive,but if you are able to harvest mature seeds and save them indoors,then you most certainly can replant from your crop.
Seedpods that are almost mature can be removed from the plants and the stem placed in some water in a sunny window to finish ripening indoors,before they are turned into 'mush' from the autumnal freezes.
The day flowering species may produce seed that will successfully overwinter outdoors depending on the exact species and your climate zone.
The seeds from Ipomoea tricolor cultivars like Heavenly Blue,Flying Saucers,Blue Star,Pearly Gates and Wedding Bells will not survive outdoor colder zone freezes,but can be harvested,stored indoors and sprouted in the Springtime.
Day Flowering species like Ipomoea hederacea,Ipomoea nil and Ipomoea purpurea will usually survive the winter of colder zones and readily reseed themselves.
Enjoy your various Morning Glories!

I have a question:
I just received some moonvine and morning glory seeds that I ordered off ebay. They are very large. The moonvine are tan colored and about the size of a small nut. The morning glory are black and about the size of 1/2 a pea. I have done MG's before and don't remember them being this big. Are these some sort of husk that I have to remove from the seeds. Or should I soak or nick them or what. I also received moonvine via a trade on this forum and it's much smaller and looks nothing like the others so I am confused. HELP!

tastefullyjulie - there are moonvines and MG's with both large and small seed as well as having lighter or darker coloration,...so rather than try to guess at the large number of different possible types,...it might be easier to post something of the description of the plants you bought,and I can try to offer an opinion if the seeds seem to match the description...if the seller has the botanical name listed correctly,then matching up the seed characteristics should be easy...a good description of the plant and flower should work just as well...

So far it sounds like the first moonvine you mentioned is Ipomoea alba,the second MG sounds like an Ipomoea nil and some additional description of the one you received in the trade would be useful to help you determine what species it is...

For growing them,nick a little bit into the seedcoat and soak them for a day in warm water...you can start them indoors in a sunny window about 6 weeks before the last freeze or wait until the weather warms up to plant them directly outdoors...

TTY,...