Yes, this is OK. In fact, it is how it was designed. This action never changes ID of customer. Customer ID parameter is used to figure out 'what' customer should be modified. In most cases, this should be bound to ID that trigger provides. Every trigger provides different set of data. For example, trigger 'After record has been created' provides information about created record (for example customer), including its ID. Trigger 'Before record is created' will provide similar data, but without ID -- record is not stored in database yet, and therefore ID does not exists. Trigger page view will provide information about page that visitor just opened.
It's important to understand that Trigger and Action are not strongly related. You can use any trigger with any action, really. For example, you can create rule like 'If somebody visits url that contains word wheee then assign customer with ID 23 to group Visitors', and it would work. It doesn't make sense, but it would work just fine.