I have the same AT on my 2001 3.0i. When I changed my ATF a few times in 2014, I did the exact same thing it looks like you're doing. I started at the blue label on the AT itself, followed that part number, believing only BMW information, being doubtful of everything unsourced I read on the interwebs, and ended up basically with the same answer it sounds like you've come to:

DEXRON VI is the new BMW-specified fluid. No, I'm not talking about ZF AT's, which are completely different. Just the GM ones.

DEXRON is a trademarked specification, rather than really a brand. GM owns it and will certify fluids that meet the spec as such. GM (their subsidiary, Hydramatic in Strasbourg, France, right across the border) actually made your transmission, in case that gives you more faith in GM vs. BMW if forced to choose whom to listen to. So in theory, you should be able to use any DEXRON VI certified ATF.

Be careful about fluids that say stuff that sounds similar but is different from this. For example, "meets standards for vehicles that specify DEXRON VI" and "equivalent to" are not the same as saying "This is DEXRON VI" or "... certified."

So you could probably get your DEXRON VI at Walmart, or you could get it at your BMW dealer and figure on drinking enough of the free coffee to make up for the price difference. If doing the latter, I recommend doing it in the morning.

BTW, this was for my 2001 I got in late 2014 at about 168k miles with original ATF still in there. I very carefully researched everything and ended up doing a total of 3 ~7qt drain and fills, including two new filters, over the next ~4k miles, all with certified DEXRON VI (I used Castrol brand, at a good price, and conveniently available at my local Pep Boys). Dramatic improvement following the first change, and still running great now at 187k miles.

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2001 X5 3.0i, 203k miles, AT, owned since 2014