Flying8764, you are correct. A NOM is a NOM and you only need one no matter the source. But, having more than one increases your odds for an appointment.I have read it doesn't matter who nominates senator or congress as they both have the same weight, a nomination.
No significance other than you know you were good enough on your MOCs slate to get all 4 nominations. Getting the senators NOM is more impressive since you had to be better than many more applicants.