Oh, sure, by default DC will not put in a lockup latch for a single clock b-level scan chain. But there is a switch you can use to insert a lockup at the end of each chain, which is probably a good practice if you're going to be stitching them together at a higher level of hierarchy. I'd hve to lookup the name of the switch...
However, it also sounds like you're asking about clock inversions in your scan chain. DC will, by default stitch up all the negedge flops together in the front of the scan chain, before all the posedge flops, so you will have exactly one place where that inversion takes place, and you don't need a lockup there.
There should never be a place in your scan chains where a posedge FF feeds a negedge when a tool does the stitching. However, if you create that situation manually, adding a lockup may or may not help. Be careful.
John
**broken link removed**