Are you using this in EQBC? Seems like you might be. If that is the case, the toon sending the command conducts the if statement, not the toon receiving the bc. Still, it should work the previously mentioned way because the data is parsed by the one sending the information.
IE: Toon sending command says /bct toonname //if (${Spawn[TankNameHere].ID}) /moveto loc ${Me.Y} ${Me.X} ${Me.Z}
then the toon sending the command parses the data. Assuming they aren't in the zone it should send the following through eqbc. Execute command ~ /if (NULL) /moveto 10 15 20
whereas if the tank was in the zone /if (1234) /moveto 10 15 20
Alternately your hotkey could be setup to do /if (${Spawn[TankNameHere].ID}) /bct tankname //moveto ${Me.Y} ${Me.X} ${Me.Y}
Either way you do it however it will parse the information on the toon sending the command.