The mule-dragons are a rare but extremely powerful type of dragon. They have a supernatural ability to seek out and hoard expensive shiny stuff like gold, silver, and precious stones, which they do near-instinctively. They will collect their riches through any available method, such as digging through rocks, or stealing from weaker beings. They also have human-level intelligence, can use language relatively well, and even have a small level of creativity and inventiveness
However, despite their human level abilities, they are still very non-human and cannot speak human languages. This, obviously, would be a significant obstacle towards doing anything with their riches. There are also a small number of humans who are able to understand dragon languages
The world they live in is, in terms of its societies and economies, the same as the real world today. These dragons, due to their low numbers and sparse spread, rarely encounter each-other and so cannot do much intraspecific trade
Could these dragons realistically buy, sell, and generally participate in human economies?