clientareadomaindns.tpl understanding

[Arsen]

Hi!
[TL;DR;]
 - can addon module manage dns?
 - my current template redirects clientarea.php?action=domaindns -> to clientarea.php?action=domains
how WHMCS understands if the dns management for the domain is available or not?

[detailed]
I want to build a module which will provide integration with 3-d party service to manage dns and email forwarding, but struggle to understand:
1) should I use WHMCS standard interface for DNS management or provide custom one? (clientareadomaindns.tpl and clientarea.php?action=domaindns)
2) I see that registrar modules should declare function `registrarmodule_GetDNS`  and `registrarmodule_SaveDNS` but will this work for other modules?
Documentation says that clientarea will have the view to manage DNS if registrar provides it https://docs.whmcs.com/Domains_Management#Clients . But there may be more then one registrar, where some will provide and others - not and there are 3-d party modules like cloudflere that provide independent dns management solution (does they just ignore WHMCS standard dns management template?)

Can't figure out how WHMCS resolve this:
- Registrar may not provide dns management
- Registrar may provide dns management, but admin configure other default nameservers
If whmcs admin activate my addont integration module and fill my nameservers as default - how


I have run into this two posts but they haven't clear much to me.

Sorry if the question is messy, any hints and links are much appreciated! 
Regards and Thanks!