Yesterday, an incredibly kind bride that I am working with asked if I would like to eat the meal that the caterer would be bringing to the wedding, or if I would like something special ordered in. This reminded me of a story that I wanted to tell, from a vendor I talked to several months ago:
The vendor I was talking to has worked at over 100 weddings, and the nature of his business means that he spends all day and evening at the wedding venue. He goes to each venue early in the day, sets up, and stays often until after midnight. He figures he's been fed about 5 or 6 times at a wedding. That means that 5% of the time, he eats during his 10-14 hour shift. I wholeheartedly believe that couples are not stingy or rude, but simply have so much to think about on their wedding day, they don't think of it to order an extra plate for their vendors.
I include a meal in my contracts, because I know I won't have time to run out and pick something up to eat. I'm usually busy from early in the morning until very late at night, and I simply do my job better when I'm fed. When going over contracts with clients, this point often causes a new discussion on which other vendors should be fed at the wedding.
Pretty much, anyone who will be there over meal time should be offered a meal. If your photographer or videographer are staying for the reception, they should be fed. If they are staying just to take photos of the room and then going home, then it's not necessary. DJ's should receive a meal, as well as the MC if you are hiring one. Wedding coordinators, band members, and the people running the photo booth will usually require a meal. If you aren't sure, simply ask.
To cut the costs a little bit, some venues offer "vendor meals" which are the same as regular meals but without the salad and without dessert. You can ask the catering manager if there are other ways to bring down the cost.
I've been at weddings where the vendors have their own room to eat in, and I've been at weddings and seated at a guest table. If it's possible, it's a nice touch to have the vendors sitting together in the main room. From a coordinators view, that way if something goes wrong/needs attention, I'm right there. The meal is also a good time for me to go over the schedule for the rest of the reception with the MC and DJ if needed.
As I said above, if you're not sure in a particular case whether to feed a vendor, or where they should be seated (for example, should the DJ sit with all his equipment, or at a table?) just ask - they will let you know what the standard is for their profession.