Nagios configuration question

I work with several small companys that have IT issues. I have decided to see if there is a way for me to monitor thier site from my location with Nagios. We are talking over the internet monitoring, NO VPN point to points. they each have asa 5505 firewalls so I could setup a vpn tunnel but I dont want them to have access to my site.

Two sites are 10.101.1.x
two sites are 192.168.x.x ip ranges.

I have a nagios server setup at my site which is a 10.101.1.x site. i am monitoring my services and network. now I want to add in the other 3 sites.

will nagios do this?
if so can you list the location in the documentation, or site in which i can find the steps to take.

Thanks in advance.