I want to replace the idler arm. The new idler arm I bought made by Precision has this instead of a dust boot.
Could I use this or do I need a dust boot?
If this is the one made for your Hummer, there should be no issue. While I've not see a cover like this, I can see how and why it will work just fine. The idea is to keep the dirt out and the grease in. With the corresponding arm (or whatever linkage piece fits onto this) pressing down on it, it'll do a fine job.