It's very unlikely since it uses a random number generator to reduce the p(collision) by 90% and collision only occurs if the first 3 hex chars were == in the source block ids having the same category but being in different courses with the same org & old-course-id but different block ids (p = n/(16^3) where n == ||course.category|| assuming our existing name guids are randomly distributed). We can control the p(collision) v readability (# of appended hex digits) if it's a problem. (Worst case would be m courses with same org/course and where every problem's guid starts with same 3 chars and where the randomint picks the same sequence; so that every attempted new name collides causing each id to become as long as the number of previously mapped problems from these courses which is n^2 for n problems.) It'd be easy enough to answer the how-non-random-are-our-guids question if that's seriously a concern (query mongo to get the first 3 chars from every '_id.name' where '_id.name' is a guid (32 char hex)).
Furthermore, because existing mongo doesn't work well when 2 courses have the same org/course, I don't believe this is a serious likelihood. (Old mongo cannot tell which course instance a given module belongs in in this case except by traversal of children links and has no safety code to prevent guid name collision)