I grow and graft Oshio Beni here in Zone 9 without any problems. It does not like anything close to full sun even here, so you will want to provide a good amount of shade. I wouldn't worry to much about the temps, just the sun and wind.
Steven

Well, first, isn't Monrovia Nurseries located in SoCal or somewhere down there? Can you contact them somehow for their recommendation? They are well-established growers with a good reputation. I can't imagine they would be adverse to giving a little advice.
Second, any Japanese maples growing anywhere near where you live? Like in a neighbor's yard? A park? A school? An office complex?
Maples are pretty tuff trees and pretty adaptable too. And even the generic green-leaved Japanese maple is a nice tree. The specialized cultivars all have their extra appeal (leaf shape, variegation, size, etc.), but the rootstock is usually your generic Japanese maple.

I have grown a Bloodgood in Inland LA area, Diamond Bar, and I think that is much hotter than San Diego. It seems to do just fine. But I make sure they only get morning sun and plenty water in hot temperature.

I have Oshio Bene in 9B, maybe 2 miles from zone 10. It has done well. The first couple of years it looked pretty sad, but then it took off. 2 foot at purchase in 2003, it's about 12' this year. Last year:

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Of course the leaves don't color up in fall--they turn brown and fall off. Mine is on the north east corner of the house and gets sun until 3 or so. If you keep the root system well mulched it will help.