Cherusci is the Latin form of Cherusker, which is a German form. The Latin form is used in English.

That the name Arminius is identical to the modern name Hermann is not certain. The German name Hermann about 2000 years ago, at the time of Arminius, would be something like Harjamannaz. Of course, Arminius is very probably a Latinisation of a Germanic name, and Harjamannaz is one option, but not the only one.

Here is a good account of the history of Arminius: http://www.webcom.com/~lstead/March94/Hermann.html