Do you provide a VPN client for end users for the point-to-site connectivity or are they still using another third party? 

Aviatrix has its own VPN client with added benefits like SAML, but you can also use OpenVPN clients as well. 

Is there a NAC module for Aviatrix VPN clients? 

We can enforce the minimum version of the VPN client that the user uses. But besides that, there are no other NAC functionalities today. 

Is transit traffic not possible with the Smart SAML VPN? 

Once the user is on the Aviatrix backbone, they can access all the resources.