As I understand it, when you use a cooker to can you may have some issues. The times typically given for pressure canning take into account the time it takes a canner to heat and come to pressure, as well as release times. A cooker might come up to fast and release too fast.
You can use a canner to cook in, though some are quite large and might be inconvenient depending on what you wish to cook.
When dealing with canning I, personally, would not be willing to cut corners on equipment. If the manufacture doesn't say it is appropriate for canning I would not use it.