Thanks to @Purity_the_Kitty, I've reworked the article on Artemis.
Lock time improvement is applied to all launchers equipped, including ATM and SSRM. This stacks multiplicatively with TAG and NARC (so 0.5*0.75*0.75 instead of 0.5-0.25-0.25. No instant locks.)
Missile Spread is hard to determine, but it seems to be launcher-specific so that does NOT improve with artemis, unless the launcher itself is affected by it.