It is not my culture so it isn’t my place to answer; however, I would venture to guess that non-indigenous Hawaiians doing the hula is cultural appropriation. I wouldn’t make the statement you have made that all Hawaiians encourage white people to engage but the one’s that do have their own reasons for doing so and it isn’t my place to comment on their choices. If an outsider is invited to participate in a cultural activity by the people of that culture, that is not appropriation. Appropriation would be outsiders doing the hula on their own and doing so in an unauthentic way.

Why might some people choose to invite outsiders into their culture:

• To establish a sense of familiar compassion with the settler/tourist. Fear of the unknown leads to oppressive behaviors so if the settlers get a taste of indigenous people’s culture they might be more inclined to act compassionately towards them.
• For representation and recognition: a way of preserving culture is to spread the educations about it. Perhaps settlers will bring with them their media and thereby giving indigenous peoples a chance to be represented in the media.
• To establish alliances with the settlers they know they cannot be rid of.
• etc