The short answer is no. Currently, there is no way to buy UBT directly on Coinbase.
However, there are a few indirect ways to do so.
The first way is to buy Bitcoin or Ethereum on Coinbase and then use a different exchange to buy UBT with those Bitcoin or Ethereum. This is a bit more complicated, but it can be done.
The second way is to use a service like Changelly or Shapeshift. These services allow you to convert one cryptocurrency into another without having to create an account or go through a long process.
So, you could convert your Bitcoin or Ethereum into UBT using one of these services.
In conclusion, there is no direct way to buy UBT on Coinbase at the moment. However, there are a few indirect ways that you can use to get your hands on some UBT.