I am no expert on chimneys, but having a liner is better than not having one at all. A liner will seal any potential gaps or breaks in the chimneys mortar, which will keep sparks and gasses inside---better for your home.
My coal stove vents into a very old, non-lined masonary chimney, which is also used by my oil-fired furnace. Both situations are not legal in my state (probably not any other state, either). However, being a frugal do-everything-yourselfer, I won't be doing it the "right" way until next year. I've already spent FAR too much money just to save a couple tanks of oil this winter. The chimney has a strong draft, even in warm weather with a cool chimney, so I'm not overly worried about safety issues. Plus, coal doesn't continuously shoot sparks up the chimney like wood does.
My parents burned wood for 30+ years in their house, which had a lined chimney. As a kid, I used to see that stack gauge regularly hit over 800 degrees, and they never had a chimney issue. My father climbed up there every spring and cleaned out all the creosote.
My chimney never sees more than 300 degrees. The coal vents much cooler than wood, and produces no creosote. The stove stays hotter for much longer. I love it, but it's intial cost is putting the hurt on...
With a lined chimney venting only the stove, you should be set.