yes you can.
Spoiler Alert, click show to read:
this is a screenshot of my ayubbid campaign in 1.05 that i posted a while ago. you can clearly see the two forts on the silk resources. one of which is selected and full of merchants as you can see at the bottom. let me asure you that all of them generate income. also all of them pick up monoplist and other traits. the income of my merchants was nearly the same as my trade income in that game.