When a person recognizes his sinfulness and flees to Christ for the forgiveness of their sins, they believing in God. It is this belief alone that saves:
If you declare with your mouth, “Jesus is Lord,” and believe in your heart that God raised him from the dead, you will be saved. For it is with your heart that you believe and are justified, and it is with your mouth that you profess your faith and are saved. As Scripture says, “Anyone who believes in him will never be put to shame.” (Romans 10:9-11, NIV)
The basic formula for salvation, faith in Christ, might seem to allow the possibility of faith in more than one God, but properly speaking I do not think it does. Here is why.
First Christ, which we believe is represented as a single mediator to the One God:
For there is one God and one mediator between God and mankind, the man Christ Jesus (1 Timothy 2:5, NIV)
Second, faith in Christ is not to be understood as based on our human apprehension of Christ, but a knowledge that the Spirit reveals to us that we are enabled to believe. We can see this is the very first and famous confession of Christ by Peter.
“But what about you?” he asked. “Who do you say I am?”
Simon Peter answered, “You are the Messiah, the Son of the living God.”
Jesus replied, “Blessed are you, Simon son of Jonah, for this was not revealed to you by flesh and blood, but by my Father in heaven. (Matthew 16:15-17, NIV)
As faith is obtained not from human reason but revealed by the Father it only makes sense that the Father reveals this knowledge truthfully, that is the one mediator between man and the one God.
Third, it goes without saying that Jesus is the mediator sent from the God of Israel. This means God the one and only who created all things.
Fourth, faith in Christ is faith in God.
That is why we labor and strive, because we have put our hope in the living God, who is the Savior of all people, and especially of those who believe. (1 Timothy 4:10, NIV)
And we notice Peter's exact confessions was “You are the Messiah, the Son of the living God.” Peter did not say your are a savior of some God, but the long awaited Jewish Messiah, who was the Son of God.
It seems a basic understanding of Jehovah in man, i.e. the Christ, must be believed in to be saved. However faith in One God without trusting in Christ can never save anyone (James 2:19)