Meteor on the Frontend, Express on the Backend (NodeJS)
By backend, I am referring to the data processing off a job queue like Kue/Gearman
As this sounds like a rules/processing engine uncoupled from the "front end" that delivers both the "clientside HTML/CSS/Javascript" and the "serverside node/database" what I think may well serve your needs is a DDP client that can subscribe to the meteor server-side publications and queue up the jobs accordingly (using an engine such as Kue).
Such a client could live completely independent of the Meteor app in its own environment. This way, you can still leverage all the reactivity goodness you seek in Meteor, yet use more established processing tools for queue-based jobs that run independently of the UI. With the DDP client, you can also hook back into the UI to inform clients when jobs complete by leveraging the subscriptions.
Here is a node DDP client that may prove helpful.https://github.com/oortcloud/node-ddp-client
Hope this helps!