To whatever degree you choose to incorporate the constructs of project management in delivering documentation and online help, focus on ensuring the project team is not surprised by what you are (or likely are not) able to deliver.
If you are in an organization that values project management, you likely have processes that allow you to plan, manage, and deliver documentation and online help required to support a product release. Defining the set of deliverables then becomes a required component of the planning process. As adjustments are made to the overall project plan, keep the list of documentation deliverables updated and inform affected groups of the change. This is particularly important if a change management process is not available to you.
In addition to customers, groups within your organization may be adversely impacted by a change in the set of documentation deliverables packaged with a product release. For example, sales people may not be able to describe feature functionality, front line support may not be prepared to take customer calls, deployment teams may not be able to install and configure the product, and training may not be able to create instructional materials. Communicating a change in deliverables sooner than later will allow affected parties enough time to assess impact and implement a contingency plan, if necessary.
This is particularly important in organizations that use a reactive model or follow loose project management. In these scenarios, you may struggle to deliver documentation on an ad hoc basis. To offset the difficulty of identifying a finite set of deliverables for a future moment in time, maintain a list of deliverables that best reflects the data available to you today. Share this list with the project team and any affected parties whenever enough data changes that requires you to modify the list. Be prepared to correlate the data changes with your list, which may have the additional benefit of demonstrating the high cost of late cycle product changes.
Consistently avoiding surprises will help establish the documentation team as a reliable, organized, and well-managed member of the project team.