For the most part, yes. If your DJ or photographer owns their company, you don't need to tip. If they're employees of a company, you should tip 1520. Caterers should be given a tip which they'll dole out to staff, and your venue should get a similar tip, assuming they have staff working the day of the wedding at your actual event.
It depends. I asked my caterer if gratuity was included in the service charge, and she told me that it was all there, no need for extra.
But I have also read, that if your photographer or dj or whichever vendor actually owns the company, then a tip is not necessary. While if these vendors work for a company then a tip is expected.
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We're tipping everyone, even the photographer who is the owner of the company. All our vendors have gone above and beyond to make this process as easy as possible. They deserve the world!
My caterer included the gratuity in the bill, so you should check and see if yours did. All of my other vendors are owner's of their companies so luckily I won't need to tip.
Re: Tips