Short answer: Yes!
Long answer: Your testing should not be dependent on Appium, but rather on your language of choice and the testing framework that you use. You don't give either, so I'll use mine:
I use Ruby, my testing framework is rspec, therefore I create a method in spec_helper.rb:
def clear_data
`adb shell pm clear my.wonderful.app.package`
end
Now in my test I make sure to do this:
before(:all) do
clear_data
end
So if I have tests that don't need to clear data, no problem. Otherwise I'll clear it before my tests. Note that I could also do a before(:each) if I wanted to clear data between tests in a suite.
Note that this is an oversimplified example to keep the discussion on point.