Your information is basically sound. Serotonin and dopamine are both neurotransmittors that are connected, in different ways, with positive feelings or elevated mood. The buzzword for dopamine (in this context, as it has many functions) is "reward" - the presence of dopamine in the brain modulates the feeling of satisfaction from achievement, and encourages people to pursue the course of action that produced it. Meanwhile serotonin has been linked to positive moods, for example in clinical depression which is often treated with medication that affects serotonin action in the brain.
OCD has traditionally been linked to serotonin, as it is classified as an anxiety disorder and sometimes treated with antidepressents. However, there has also been research linking certain kinds of OCD to an imbalance between the functions of serotonin and dopamine (see for example
The role of dopamine in obsessive-compulsive disorder: preclinical and clinical evidence). From what I have read, research on this subject has led to the use of antipsychotics in treatments, in particular in cases where patients don't respond well to SSRIs (antidepressents) alone.
In summary: yes, there is a connection between dopamine, the "reward chemical", and obsessive compulsive disorder. It appears the connection is stronger or more apparent in patients who also have Tourette's syndrome. With respect to genetic markers, as far as I know the genetic research is in an early stage. It cannot be said that any one gene "causes" a specific illness, only that there is a statistical link between them. Correlation does not imply causation, and genetic researchers are unlikely to say that a gene causes an illness if they can't demonstrate a mechanism by which it does so.