IS Boxer macros (like other addon macros) can be 1024 characters long, so [nodead, harm, target=arena1] won't be a problem, as far as macro length.

If you are building a macro inside of IS Boxer, you need to give it a unique keybinding.
Which is not the hotkey to activate the macro.
It needs to be something, which is free within warcraft.

Then again, you could accomplish this entirely with keybindings, and warcraft based macros.
Put your windshear macros in wow, one per shaman.
And give them a keybind somewhere.
And then your normal macros in wow too.
And then have each of the FTL DPS Keys, do:
a) FTL Assist Me;
b) Keybind for Wind Shear wow macro;
c) Keybind for your DPS key.