In Github, is there a way to search for pull requests created by any author from a provided list?

Make sure that you are using the full search at https://github.com/search.

Then simply add extra author: <name> fields to your query. The searching engine will OR fields. For example:

is:pr author:username1 author:username2

(Note that this only works on https://github.com/search. The search syntax on other pages, like https://github.com/pulls, is severely limited and does not support searching by multiple authors. If you try the same search on https://github.com/pulls, GitHub will simply ignore all but one author that you list.)

To limit it to repositories by a specific owner, add the user: <owner> field to the query.