If you choose to take advantage of the Harris County weed program and... are riding dirty (it is still illegal and I always advise people to follow the law), you should make sure you don't have a gun.
To give you an example...Say Chamillionaire is driving around and he gets stopped by the cops. He has weed. Cops find it. He meets the MMDP criteria I spelled out in Part 1. He would be eligible for the Harris County Marijuana Program and he could avoid arrest and charge.
Now say Chamillionaire is driving around with a gun. He doesn't have any illegal substances. Cops stop him, they find the gun. This isn't illegal provided that he is in compliance with the various Texas and Federal firearms statutes (a lot of material there, maybe for another post.) He does not get charged with anything.
Finally, consider this third scenario. Chamillionaire has a gun and weed in his car and the cops find them both. The penal code makes possession of a firearm illegal if you are engaged in "criminal activity." Possession of weed is "criminal activity" so he is now unlawfully carrying a firearm - a class A misdemeanor. Since there is a gun present, he wouldn't be eligible for the MMDP program (see part 1 for eligibility requirements.) This means he gets charged with the Possession of Marijuana case too.
So there you have it. You can ride with weed and not get arrested. You can ride with a pistol and not get arrested (read the laws...there are many). But if you ride with both, you can get arrested and charged with two crimes.
*Disclaimer: Chamillionaire was used as a hypothetical example and I have no information that the Mixtape Messiah, or any other member of Swishahouse are now or have been in fact Ridin' Dirty.