The LD_PRELOAD workaround is meant to "fix" the shellshock bug, sysdig doesn't do that, it just passively monitors every injection attempt up to the point where the injected function is actually read by a newly spawn bash.

With the LD_PRELOAD trick you can definitely secure your system, but you won't be able to see if there's a new service that is being used as an attack vector (for your own curiosity). With sysdig, you can, and if you capture a trace file you can also follow the exact process chain that caused the propagation of the environment variable.