Minutemen wandering in the wastes?

I know that when you shoot up a flare that the Minutemen will come if you're close to a settlement, but I want to know, how often do you find Minutemen just wandering around, and do the number and size of your settlements affect it?

No, i asked if it is possible to see the minutemen and the brotherhood work together in the commonwealth

In Fallout 4 you can side with four factions. The faction that you side with will become stronger and over time will begin to have an increasing presence in the Commonwealth, both in terms of random wandering parties and check points. In your instance you're obviously backing the Minutemen and have been building up a variety of settlements for the Minutemen to the point where Preston has given you flares, so the most active faction in your game will be the Minutemen and it will be this faction that is setting up check points and randomly wandering the Commonwealth.

If you side with the Brotherhood of Steel you will give Brotherhood members fulfilling the same role, if you side with the Railroad you'll get Railroad members fulfilling this role, etc.