How should I lay my engineered flooring to account for a hearth?
Most installs I have done we have trimmed around the fireplace.  There are several ways to do it.  If your fireplace hearth sits on flat ground we try to meet even - which is almost impossible unless you did the floor and hearth all in one install.

Most of the time we trim around the fireplace first and then cut to the trim.  This is very very very time consuming because you will potentially have a lot of boards meet the trim and they need to be within 1/32".  

An easier way to do this, especially if the hearth material is not as even, is to add a riser then maybe an optional board (or partial board).  So you would layout your wood and just get as close as you can to fireplace then nail down the riser around the fireplace.  The corners take some work but this is pretty easy.  This looks really good if it is brick and you can get (or notch) the riser so its back sits in a mortar line.



And a note on floating - I would probably use a riser.  Because you could set the floating wood 1/4 inch from fireplace, giving it a proper gap, and then staple the riser just to the underlying floating wood.  It would still be floating then.