Yes, a mortising bit with a top bearing can be used with a template to rout hinge mortises, HOWEVER, any of the top bearing mortising bits I've seen have too long of a carbide cutting length to be used with commercially made jigs. As an example, I have both the Bosch metal hinge template jig and individual Templaco single templates. The Bosch has a thin metal edge for a template guide to ride on and the Templaco are 3/8" thick. That barely leaves enough surface area for a bearing to ride and in operation, something's bound to go wrong ruining the bit, the template or the hinge mortise. If you make your own templates that are a solid 1/2" or greater, the top bearing bits should work fine.
Festool offers 17mm template guide plates for the router bases, so I believe a 14mm diameter bit would be ideal for that size template guide. Here are two bits that are 14mm:
FreudFestoolI think this would be similar to the standard 5/8" OD template guide mated with a 1/2" diameter cutter, both increased an almost equal, yet small amount. At some point I'll have to get them and try out the metric combo to see if it works more than just in theory.
Also, I believe Anthony was the one who pointed this out, make a small pass across the front edge of the mortise and on the right side go in a little ways, first, to eliminate tear out. You'd be climb cutting on the right hand side of the mortise.