I say yes because a person who already smokes and gets high might be more willing to try another drug to get high if marijuana is not available at the time. It depends on the person, but some people do not want to function without being high and therefore may turn to another drug to fulfill that need. A marijuana smoker is more likely to use other drugs than someone that does not use marijuana at all.
The idea that marijuana or any other drug is a gateway drug is antiquated and well refuted. The choice whether or not to use drugs, and the preferences among them, are individual choices that have to do with personal taste and personality. Preferring to use marijuana does not indicate that someone will prefer any other thing, particularly not other drugs that have completely different effects. The reason it seems like drugs may lead to one another is that someone with a more experimental personality is more likely to try any and/or multiple drugs to satisfy their curiosity, where someone that is more reserved may not prefer to try any drug at all.
I do not believe that marijuana is a gateway drug. But then again I do not believe that any one action, smoking, drinking, smoking pot, leads to more bad habits. I believe that people are lead to harder drugs by their inability to deal with their problems and trying to escape them. I know many people who smoked pot while we were in high school that either still smoke pot occasionally or gave it up all together. I know of none that graduated to harder drugs.
I've been smoking marijuana for a while now. I've never sat there and thought to go out and do harder drugs because the marijuana induced high was not enough. I do believe, however, that those who already smoke marijuana are more opt than others to go out and try other drugs.
Most people who use harder drugs all started with marijuana for a reason. Marijuana and alcohol both alter our state of mind but people are not exposed to the black market when buying alcohol. The only way for people to get marijuana where it is illegal is through the black market which includes harder drugs and crime. Legalizing marijuana can actually prevent the rise of harder drugs.