See MaxCDN for example who uses a mix of dns providers (AWS Route53 and NS1):
ns-5.awsdns-00.com. ['205.251.192.5'] [TTL=172800]
ns-926.awsdns-51.net. ['205.251.195.158'] [TTL=172800]
ns-1762.awsdns-28.co.uk. ['205.251.198.226'] (NO GLUE) [TTL=172800]
ns-1295.awsdns-33.org. ['205.251.197.15'] (NO GLUE) [TTL=172800]
dns1.p03.nsone.net. ['198.51.44.3'] [TTL=172800]
dns2.p03.nsone.net. ['198.51.45.3'] [TTL=172800]
dns3.p03.nsone.net. ['198.51.44.67'] [TTL=172800]
dns4.p03.nsone.net. ['198.51.45.67'] [TTL=172800]
Curious, are you the kind of person that runs their own smtp email server and complains about GitHub pricing being too expensive?