Not directly, the reason is that classic Nagios 3 or 4 uses a complete different approach for the service checks. Mostly active checks in Nagios compared to most checks passive in CMK.
What you can do is export a list with host names and IPs from your Nagios system and then make a mass import with this csv file in to CMK.
Now you can assign the proper configuration for every host (SNMP community if needed, agent type and so on).
In the end there are many manual steps and the only “migration” is the host list and IPs are the same
To do such an export i installed the livestatus broker module in my classic Nagios systems and made a livestatus query to get all hosts from the system. This is now some years since the last time a needed to do this. I don’t know if there is a broker module available for the actual Nagios 4. For Nagios 3 it should be no problem as these broker module is also used inside the CRE.
With this you could also export the group assignments. But i don’t know a way to automate this then for an import.
To get a good overview what you can do with livestatus you should consult the manual here.
Small guide how to install livestatus inside an Nagios4 on Debian
In the end livestatus is the key to migrate config data from an classic Nagios to the outside.