Above the Law performs the useful service of identifying the 2017 law school commencement speakers. It is surely not comprehensive, but it is long and likely representative, because the site solicits information as well as doing its own reporting.
Of the politicians and political appointees, current or former, who are speaking this year, 22 are Democratic elected representatives or officials appointed by Democrats. Two are Republicans. And it is clear that there is close to a rule for choosing Democratic speakers as opposed to Republicans, because the exceptions prove the rule.
You can be a Republican official and a law school commencement speaker if you are Vice President of the United States and your university has a very long established practice of inviting the newly elected President of the United States to be its commencement speaker at its university wide graduation. But because that President was in its view the unacceptable Donald Trump, Notre Dame invited Mike Pence to be the commencement speaker. Now I am not as confident as Above the Law that he is a speaker for the law school itself as well, but even if he is, it is on account of unusual circumstances.
The other Republican official speaking is Alex Acosta at the Florida International University College of Law. He is now Labor Secretary. Until April he had been Dean of the Florida International University College of Law.