
Unfortunately 95% of cross breeding with pedigree breeds isn't done using health tested patents, the breeds relying on heterosis to remove health issues.
Scientific crossbreeding(as in the American Dalmatians)is a step forward, however crosding two breeds with the same genetic/partially genetic conditions is a retrograde step , especially if one or both breeds used have other genetic conditions as this introduces these as carrier conditions to the F1 generation & actual conditions to F2 & subsequent generations.
If(& it is a big if)any dog intended for use in breeding & it's siblings( for polygenetic conditions)were full health tested before being bred from & only those with totally normal results used, it wouldn't matter what cross was used, they would be some improvement.
If you mean using another breed to improve the health of another, then this is a multigeneration breeding program to improve the breed's genepool & not an easy or cheap option.
Take a quite closely bred breed like the showline border collie, what breed would you use to open up their gene pool that doesn't have common genetic conditions ? ALL the collie breeds have common conditions so it cannot be another collie breed. If you use a non herding breed you will lose the function for which the breed was developed for. It's not as easy as some believe.