Is it good practice to Use the main webhosting server as ns1 in the likely event of a DOS attack?

i note that in many tutorials we are directed to setup our main webhosting server as ns1 and a second virtualmin instance as ns2.

in the age when DOS attacks are a major concern, is this actually good practise?

for someone going out on their own with a webhosting business (albeit a very small startup), should i instead have a minimum 3 server setup or it is quite ok to go with the 2 server model as outlined in the BIND DNS tutorials? (ie web hosting server, ns1, ns2)

 

if you don't need external DNS services e.g. from your domain registrar and thus need your own using ISPConfig well... depends:

DNS is likely to be attacked
DNS on primary server with other services ... yeah bad
Secondary Servers in ISPConfig ( afaik ) currently suffers from no DNSSEC-support ( only primary server has it ).