Karla Arboleda recently published an article in Vegetable and Specialty Crop News, Wildflowers Help Watermelon Pollinators. In it, she reports on conclusions reached by Miriam Jenkins, a graduate of Clemson University’s Wildlife and Fisheries Biology program. "For greater fruit quantity and quality, growers can use wildflowers to attract watermelon pollinators."
During her four-year study, Jenkins found "59 species of wild pollinators that pollinated watermelon flowers in 21 different fields." Surprisingly, most of those pollinators were insects other than honeybees. "Honeybees were only pollinating about 25 percent of the time."
That's encouraging, since honeybees have been suffering a lot recently due to environmental stresses, diseases and predators. Keep in mind that wild pollinators were in North America long before honeybees were introduced by colonists.
It stands to reason that if wildflowers are so important for watermelon pollinators, they are as important for other crops, too. So far as I know, there are no pollinators who only visit watermelon patches.
You can do your part to ensure pollination success by planting pollinator-friendly flowers. Not only that, you should consider all flowering plants as being helpful to the cause - even weeds. Instead of eliminating weeds around the perimeter of your garden, maybe leave them alone to flourish at a distance.