No, these fake meats are not necessary for a good vegetarian diet. In my opinion, they are mostly not tasty, fatty and not healthy. Also, heavily processed food, like they often are, reduces the positive effect a vegetarian diet has on the planet.
There are tons of great vegetarian bbq recipes in the net. I especially recommend stuffed mushrooms or pepperoni (add chickpeas or lentils). Most often than not, meat eaters loved them. Or baked (sweet) potatoes for something more classic.
For me, the main downside is that it takes way longer to prepare than simply pulling some (fake-)meat out of a plastic package.
To occasions other than a bbq, I often bring vegetarian "sushi".