I don't know if the scanners are worldwide universal, but the scanners will tell you what company your chip is thru, then they would contact the company and notify them and give a description of the dog.
I know the clinic I worked at read AVID chips (b/c that is what was mostly used in that area), but if it was thru another chip company, it would show the first 4 #s (I believe), which tell you which company it is thru. And this was several years ago for a basic reader. They do now have universaly readers, but most clinics/shelters don't use them. As for the European frequencies, I believe they are not allowing them to be sold here. But I'm sure in the future, there will be a worldwide frequency.
The only reason I don't like tattoos as much is that they can fade over time and get hard to read. Especially for dogs with dark skin. This was the case even in dogs with new tattoos at CCI where I worked.