By a literal reading of the cards, yes he can use the 5 instead of rolling.
I'm assuming that you are talking about the Creepy Puppet event. The real question is actually about how the Creepy Puppet event works, moreso than how "It is meant to be" works.
The player on your right rolls a might 4 attack for the creepy puppet. If you take any damage from this attack, the explorer with the spear gains 2 might (unless you have the spear).
I think what you are misunderstanding is how the Creepy Puppet (same with the Bite Omen) works. The attack is still rolled; it's not that he just automatically gets 4 attack power. He rolls 4 dice. If the card just said that he's attacking with 4 damage, then he couldn't use "It is meant to be", because that only applies when rolling. But here we have a card telling him to roll some dice, and another card that tells him that on a dice roll, he can choose to use the 5 instead of rolling dice.
Note that he has to make this choice BEFORE you roll your defense though. So he doesn't know if he'll get any benefit out of using his 5; so it's a risk for him.
Now, there is a good argument to be made for the opposite conclusion (something that unfortunately can happen in Betrayal). When it says "the player to your right rolls a might 4 attack against you", it's easy to read that as being that the player to your right is just being used as a means of having the game itself roll dice; it's not really "his roll". It's the Creepy Puppet's roll, the player is just the physical means by which the roll is made. By that logic, he couldn't use the It is meant to be; because that can only be used on his rolls.
So the question is whether you want to be completely literal, or give a more relaxed interpretation of Creepy Doll (and Bite).