I have been to Vero Beach one time, and it was last year sometime in the third week of May. The love bugs are not there for the entire month. The scourge apparently lasts for about a week, but the timing of it can vary each year. I have been told that it never occurs after June 1st.
When I went, I was there for four days in a 1BR. And, at the outset, I should say that I think Vero Beach is a fantastic resort, and I very much enjoyed the beach and amenities. With that being said, when we were there, the first 1.5 days we were there was the end of the love bug scourge. Neither my wife nor I are afraid of bugs or bothered by love bugs in isolation. However, this swarm of love bugs over the resort was like something from a horror movie. When we went to the room, the door to our unit was completely covered with them. They were writhing all over it, particularly around the edges. When you opened the door to go inside, no matter how quick you were, dozens and dozens of them would get through and be inside the room. We called the front desk after awhile to see if there was anything they could do. Interestingly, they sent someone who used a vacuum cleaner to suck them all up from around the door. This relieved the problem for a short period, but within an hour more had returned and were writhing all over the door again.
When we first went down to see the pool area, there was not a single person there. The pool in particular seemed to attract them, and you could not possibly have used the pool. If you opened your mouth to breath within 100 feet of the pool, you would suck love bugs into your mouth. As we tried to walk through the area to get to a restroom, you could not take a single step without squishing a pile of them. The water itself was completely covered with the bodies of dead love bugs that had drowned in the water. I have never seen anything more disturbing in my life. The beach was at least tolerable because the ocean breeze seemed to keep too many of them from accumulating, but they were still there and noticeable.
By the end of the second day, we were ready to leave and go home. But, just as we were making preparations to do so, the scourge seemed to suddenly and magically dissipate. They were not all gone immediately, but we could get in and out of our room. By the morning of the third day, we could use the pool and the bugs were barely noticeable. This was extremely fortunate, because we found out over the last two days that we love the resort, and I would definitely come back. But, personally, I would never come back in May.
I am not telling you not to go. Given your dates, they might not show up until after you leave. But, if they do show up, I think you should realize what you are in for. Best of luck...