This will depend on the individual landlord.
Guarantors are usually required by landlords (or letting agents) in cases where the tenant might not have enough income to pay their rent. People on benefits are very likely to have low incomes, which means they will often be asked to provide a guarantor.
Some landlords (or letting agents) may have policies that mean they will always ask you to have a guarantor if you are on benefits, regardless of the rental amount or your income. Others may only ask for a guarantor if you cannot prove that you can pay the rent.
OpenRent has no ‘blanket policies’ or hoops we need tenants to jump through. We allow tenants to deal directly with landlords. So if you and the landlord reach an agreement without a guarantor, you are able to rent the property.