After coming across Frumentarii in Wikipedia, the Ancient Roman secret police / intelligence agency that started off as a courier service.
I sometimes wonder if the Redcaps may be heading in that direction. Then I recall some details from AtD, and I suspect House Tremere would desire this.
Redcaps are already information gatherers and (in some ways) agents of the Order, at least in relation to the world outside the Order. I see House Mercere as more organized than the Order at large, although not as much as House Tremere.
I suspect the two Houses have cool relations overall.
House Tremere and the redcaps have a quite cozy relationship in the Transylvanian Tribunal at least. Of course, half of the redcaps there are not officially considered redcaps by House Mercere. (The non-official ones are mainly family of the official ones.)
Overall, House Tremere would prefer that there were more redcaps.
Overall, House Tremere would prefer that there were more redcaps working for House Tremere 
I suspect the attempt by House Tremere to subsume Redcaps is rejected by House Mercere. Maybe I've missed something in Against the Dark.