Tim - not sure whether you saw my comment above in "lost in translation" but as I noted there: 

 "Vanuatu" a book published for independence by the institute of pacific studies. The book is written in 3 languages - Bislama, French and English. The forward is written by Walter Lini (who I believe was the first prime minister) and it says "This book is the story of our achievements. This book is the witness to our victory. This book is the celebration of our history and our victory. So we say, In God is our history, in God is our victory and in God we shall have victory. Vanuatu stands in God, lives in God and moves in God. This is what we mean by 'In God we Stand'". The final sentence of the corresponding Bislama section reading: "Hemia nao mining blong stamba toktok 'Long God Yumi Stanap'" 

 I wouldn't profess to be an expert on english grammar but I feel this is more or less hearing from the "horse's mouth".  It was written for independence (at a time when the motto first came into being), its written by a south pacific organisation and it explains the meaning of the term.  It is possible that Walter Lini wrote his passage in Bislama and it was translated into into English inaccurately but I think an inaccurate translation is unlikely.