I have teachers who are there for their pieces/students only and work hard for them but don't go above and beyond. Then I have a non-competition teacher (a ballet teacher at the studio with no competitive pieces), who came to all of our competitions this year and worked nonstop.
A: It is best to compensate teachers for off-site hours that support any and all studio programs. This establishes the expectation for everyone that work is being done, a level of professionalism is expected and that there is a designated employee representative onsite.
We have discussed with our teachers and agreed on a $100-per-full-day stipend, and a $50 partial-day stipend of pay, plus the studio pays their meal and travel expenses. Our lead teachers who manage our dance teams work out a schedule in advance. As a studio, we oversee a lead parent volunteer per team, so that at all times we have coverage as well as a balance for everyone, and those long hours don't become too exhausting for one person to handle alone. Essentially, everyone is working long days and doing work above and beyond what they would be paid by the hour. However, since we discuss the role and details in advance, everyone is clear on the compensation for the contribution.
Some of our teachers do come to just show their support and watch. In those cases they are not paid, and we have communicated this as well.