No, it's an unsecured debt that will be bound by the IVA, it's highly unlikely you could choose to exclude it. If you enter the IVA your guarantor will be most likely expected to commence servicing the loan as you'll have defaulted by entering into the IVA. As a joint and several liability the creditor may choose to claim in the IVA and receive payments from the third party, or not claim in the IVA and rely solely on the guarantor servicing the loan.
You can't treat the loan favourably and pay it outside the the arrangement and you wouldn't be given an allowance in your I&E to do so.
If it's Amigo you're referring to, there's a clause in their T's and C's which will allow them to terminate if you enter into an IVA at which point they will most likely enforce against the third party and demand full payment immediately.