By themselves, probably not. However, depending on what you mix with them, you may see some weight gain due to an increase in caloric intake. Simply put, if you put in more calories than you expend, you’re going to gain weight. That maxim is true whether you are using a vegan based protein powder, or one based on whey protein for example.
It should be noted, however, that those who use vegan protein powders often note that they don’t gain weight as readily as other forms of protein powders. However, that is most likely because the vegan protein powders are often mixed with low-calorie liquids, such as juice or water.