Donna, I think it's not so much the heat, since the North can be awfully hot in summer, but the lack of a resting period of cool for deciduous trees in the Lower South.
See if you can find a site for this tree/shrub that indicates it's heat index tolerances.
I'm growing the regular red twig (shrubby) here in Zone
7b-8 in a northern exposure. First year so I don't know how they'll fare. Tricky siting since you want them backed up with green so the red twigs are noticeable after leaf drop.

Unless you particularly have your heart set on the Cornus (which I've tried 3 times and lost), you might consider Eleutherococcus sieboldiana variegata (sometimes still listed as Acanthopanax). This has the same delicate leaves nicely variegated, but alas, no red stems. But it's hardy, pestfree, and thrives in part to full shade for me. It does have tiny thorns but I cut it often for indoor arrangements and they are not as fierce as roses, for instance...just somewhat prickly. josh

Here is a link that might be useful: Eleutherococcus

I gwon this in Zone 7 - have ever since I got addicted to the plant thru little seedlings from Heronswood over 10 years ago. It is prettier and grows better for me than other 6-8 dogwood shrub varieties I have, including 'Spaethii' and 'Silver & Gold'. Lights up my shady spots - likes water, but will tolerate dry shade once established.
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