While I have frequently seen LabView used for instrument/hardware control, I admit I have never seen people use Simulink for that purpose. Is there a popular Simulink/Matlab add-on for that?
It can be indirectly. Addons exist to for instance convert the mathematical models described in Simulink to code (C, VHDL..) deployable to hardware targets. So, algorithms can be developed in simulink and then integrated into an embedded application without manual translation.