Installed some drop in lights the other day and noticed the whips I used to attach were labled 18/2 7amps max load. They were UL listed, am wondering if anyone knows if the listing permits a "feed thru" load (IE fixture to fixture) or is it just J-box to singal fixture only.

You really need to see the manufacturers' instructions. While the use of #18 suggests that the whips are intended to be run from J-Box to light only, some such assemblies have several circuits in the whip, and connectors designed to make the connection 'at,' rather then 'in' the fixture.