No check_host_alive howto?

Hello guy’s,
I have installed and configured Nagios for about 20 servers.

My problem is that I cannot install nrpe plugins or ping to one server.
I only want to monitor a website (check_httP) on this server.
Now Nagios shows this host as down, althrough the http service shows OK.

Is it possible to configure “multiple” check_host_alive('s)? And i mean, one check_host_alive trough ssh or http, for host1 and for other hosts the normal check_host_alive?
And so yes, how to configure it?

I’l hope you can help me further with this.