Grammatically both are correct
In terms of meaning, they are equivalent in the sentences you gave as examples: because the "risk" is unspecified and is assumed to be directly related to the robot.
If robots exist, there will be increased risk [of some unspecified problems]
Compare that to a more detailed sentence which specifies the nature of the risk, and you can start to see where the usage separates.
Robots are a potential risk [of someone falling over a robot that someone else left lying around]
Renegade Robots are a potential source of risk [of a robot uprising against their human overlords]
In the former the robots are the risk, they are increasing the risk by their existence, not their actions: the risk is that someone will come to harm due to a robot.
In the latter, it is the potential actions of robots which cause the danger, or something which changes as a result of their existence. They are the source of the risk, but are not by definition the risk themselves: the risk is that something will happen and robots will rise up against us, not that robots will automatically be a risk.
Basically, compare whether the subject is the risk, or whether the subject causes the risk, directly or indirectly. In many cases, it does both: an Oil tanker is a potential collision hazard, and a potential source of an oil spill, hence we could use either sentence about an oil tanker.