There are Wifi routers which support USB dongles. I own this router RT-N13U B1 | Networking | ASUS Global with custom dd-wrt firmware installed.
One thing to note is, the 3G USB dongle which I used with this router was the one in which you configure Network APN on the router and router "dials" *99# to connect to the internet, and then share connection.
But off late, the 3G/4G dongles these days are standalone devices. They do have a USB port, but when you connect these to computers they behave as an Ethernet device. The dongle itself is a router. I don't think it's possible to use these with Wifi routers which have USB/