Do I need to sand oil-based lacquer before painting?
It is always a good idea to sand before painting, though that is one way to do the prep work. De-glossers will prepare the surface too, although I have no experience in this type of prep. The name brand cleaner will not dull the surface, but it will help in the surface prep. If there is soot present, this is good to remove that, then sand or de-gloss.

If you chose to sand there are sanding blocks with a foam center that will help conform to the irregularities of the brick.
It is always good to prime a surface after sanding or deglazing, primer is formulated to grip the surface to hold the finish paint better. The primer can be tinted to the final color if there will be a big color change. That way the finish color has a better chance to cover in one coat.