Are you sure it is a Vaquero and not a Bisley? Ruger does not list a Vaquero in 44 mag, they do list the Bisley in 44 mag though.
Actually after looking closer at the Ruger website, the Bisley is a version of the Vaquero. The manual says you can use any 44mag round. Not sure if I would want to run a steady diet of +P rounds through it, but nothing in the manual says not to.