As a greeting or introduction, it’s basically always “welcome to” rather than “welcome at” or “welcome on” or any other such preposition.
It’s often the very first sentence in your presentation or on your website or whatever, and it doesn’t make a great impression to start with even a minor blooper…
- Welcome to our website, Welcome to my home, Welcome to this conference, Welcome to our hotel
You’re always safe with “to”
- You might perhaps use other words in a running sentence, such as We made them welcome in our home or They offered us a warm welcome on their island. But that’s not the “hi there” context that I’m talking about.
There may be plenty of other words used in running text, and probably examples of different usages, but the basic point is that “to” is okay and won’t sound clunky.
Prevalence: high. Another of these ones where non-native authors don’t try to think what the English speaker would actually say.
Frequency: low. By its very nature as an introductory text, it’s not an error that occurs more than once in a document.
Native: no. Though I’d not be surprised to see a few examples of different usage.