Hetzner has also been offering arm based macs for a while now. Maybe they don't include them in their definition because technically they're not servers?
They're not really any different to a Sun pizza box and we used them as servers back in the day :)
But I believe the mac mini doesn't have ECC Ram? I've had pretty bad experiences with non-ecc for database servers. It probably doesn't matter as much if you're only processing data where a bit flip isn't problematic or where data isn't stored aftewards (e.g. web server), but for data manipulation I wouldn't use non-ECC.