Mille and un millier de followed by a plural verb - when in the subject?

Where the lesson says "Both mille and un millier de are followed by a plural verb (sont venus)", am I correct in saying that this only occurs when these adjectives are modifying the subject? The rule is listed after a number of examples, some of which have the adjectives as part of the object/ with no verb following). Let me know if I'm missing something. Thanks!