ように見える
can often be translated as "looks like". In your case,
あの人にそんな秘密があるようには全く見えないがな
He really didn't look like somebody, who was keeping such a secret.
This よう would be this one, written 様 and meaning amongst others "look, appearance".
There are lots of questionslots of questions about よう(に). Reading some of them might be helpful as well.