It doesn't exclude anyone who would like to participate in these ceremonies. If a student says I am a black student and would like to participate they can. There is no racial purity test. If someone says I am gay and I would like to join the LGBTQ event they can.
Everyone is invited to the main graduation and these additional celebratory events occur as complementary events. For a long time graduation ceremonies were white people only affairs. Now, they are not, and in addition some groups would like to celebrate the achievements of their community on top of that. There are celebrations that are separate for Honours students, student athletes, students in different majors celebrate in their own ceremonies. There are separate ceremonies for students in programs designed to support economically disadvantaged students (EOP etc). This is not a big deal. Again, nobody is hurt by this, and nobody is told they are not welcome. The friends and family cheering in the audience will not be exclusively from the graduates backgrounds.
I suppose students could request a whites heritage celebration, but taken in the context of the racial history of the United States, I think any college or university would understand what that message was really about.
The message is if you are black, Asian, Gay, etc. then there are these additional events that you may choose, or not choose, to participate in. Who is being told no?
The real question is if you are a white student why would you want a whites only celebration? The answer to the other groups is because they are emerging from long, long periods of oppression and existing in the shadows, and want to celebrate with others who have shared experiences. That is not true for white students in the US.