Have any of you been successful growing Sea Berry in USDA zone 8 or higher?

Mine died. But I have killed most things.

Drag. Did it live for a year or more...or just croak?

Yes. We have a much milder summer that either of you will. I don't have acreage. I have a suburban lot, and it kept growing and taking over, so I had to remove it. I like it as a plant. If I had acreage, I would totally grow it here.
John S
PDX OR

I get the summer Monsoon which helps a lot.
I stuck a couple in the ground 8 weeks ago & they looked pretty good when I last checked on them 2 weeks ago. I have them planted in an area with Buffalo Berry, Hanson's Cherry, & Goumi Berries.
I wish the Seaberry plants were a little less expensive, but that's the way it goes.

There are massive Seabuckthorn trees on the Bullock homestead on Orcas Island(Washington state).

There are sizable examples in the Spring Ridge Commons food forest near downtown Victoria.

At least the latter should be solidly zone 8.