Yes but
Yes you can by using two diplexers. You would put one diplexer outside and would have the antenna coax cable and one of your dish cables into the diplexer with the output going to the existing cable running inside. Then you would put another diplexer inside at your receiver which would split the one back out into two with one going into the dish input and the other into the OTA input. The diplexer sorts out which signals go where.
I researched doing this, however the consensus was that you do lose some signal at each diplexer. This may or may not be an issue in your area and will most likely affect the OTA signal more than the dish signal. In the end, I chose to mount an antenna in the attic and ran the cable internally so I didn't have to use diplexers or drill a hole through my house.