TEM does not apply to the To Hit DR when shooting WP, and since WP is not SCW, it can be fired into all terrain where SMOKE is allowed.
C6.8:
"6.8 CASE Q; TEM: TEM1 applicable to the target must be added as a DRM to the TH DR of a shot taken on the Vehicle or Infantry Target Type or on a LATW TH Table [EXC: BAZ firing WP; HD (D4.2)]. Case Q does not apply to an Area Target Type TH DR (see 3.331). "