What I'm specifically NOT looking for is something that runs on the same server. And also I'm specifically not looking for is something that requires a DirectAdmin login to look at.
So no, this isn't for me. I believe I've written elsewhere about a small script I wrote which takes snapshots of the first few lines of the output of 'top' every five minutes and mails them to me if the load is higher than a threshold I set.
I am running nagios on one of our servers; we installed it many years ago when we only had a few servers. Now my intention is to set up a server with only nagios or munin on it, which will monitor all our servers, giving us one place to look; a place which not coincidentally, will NOT go down because the server hosting it is too busy, because that's all the server will run. I suppose there are advantages to having been in business so long that we have servers that are now hopelessly too slow to be used for our clients.
However I certainly understand how your plugin could be very useful, though in some cases of course by the time you need to check your server it will be too busy to even log in to DirectAdmin.
Jeff