No, Focus Punch is still an attack. Sucker Punch can only ever fail if either, your opponent doesn't attack you, or if they use a move with higher priority (or same level of priority but higher base speed).Does Sucker Punch fail if used on a mon using Focus Punch?
EDIT: or if they somehow have Wonder Guard and aren't weak to Sucker Punch.
And for the record, it can be used on a pokemon using Counter or Mirror Coat, as they DO count as attacks.