I think the fish dealers in your area are feeding you a line of BS... I don't know of a single pond that has a healthy LMB population that also has a self sustaining FHM population, even with heavy vegetation and spawning structure galore.

FHM simply reproduce fast, are easy eating for LMB and are loved by LMB. They just get your bass population off to a good start, but will not last more than a year or two...

There are few forage fish species that can handle LMB predation and still maintain a self reproducing population. Not including game fish species, mosquitofish or gambusia seem to be able to hold there own under just about any kind of predation level in almost all circumstances as long as they are not stocked in far north ponds. GSH under the right conditions can maintain a self reproducing population under bass predation, with vegetation cover and shallow areas to hide in. I have also had luck with banded killies. Both the killies and mosquitofish are not commonly available commercially but can be found... The GSH are sold just about everywhere.