I can't say for certain but since hummers are pretty much loners and don't travel in flocks like other birds, I doubt they send ut scouts. The males migrate first to set up a territory and then the females follow within a week to 10 days.

Penny

Gender Differences in Migration
Male hummingbirds migrate northward as much as three weeks earlier in the spring than females. In the fall, the mature males similarly leave earlier than females and immature birds. Several reasons are generally offered for this behavior:

by arriving first, the earliest males have their choice of the best territories, which improves their chances of attracting females for breeding. But this advantage must be balanced against the risk of arriving before food is plentiful.

females - who will soon be nesting - will find more and better-developed flowers on the spring migration route if they leave somewhat later; in promiscuous species such as hummingbirds, which do not form pair bonds at all, breeding females are more valuable than males, and a reliable food supply reduces their risk.

the early fall departure of the males may leave a richer diet available for the developing young of the year.
Hope this might help

Here is a link that might be useful: humminbirds