Decking should be secure, attaching one member to another in various forms of secure and strong ways that engineers have spent a lot of time thinking about, designing and manufacturing. There are reasons for that!
Deck codes change all the time. They do because, typically, there is an accident due to insufficient attachment, overload or just poor construction. Then thinking changes and they decide to change the standards to include stronger, more or different stuff!
But, everything now, from top to bottom, is securely attached to something else. Secure attachment does not include toe nails, or one member merely resting onto another, no matter how strong that supportive structure may be.
One thing decks are not made for is the HOT TUB. Hot tubs are heavy!
I understand that a hot tub that is 84"x84" can hold between 400 and 500 gallons. If I remember my 7th grade science, a gallon of water weighs 8.33 pounds.
A small fiberglass hot tub with jets can weigh 300 pounds or so. A fancy one made for 6 or 8 people can weigh 1000 pounds, empty!
ADD IT UP! HOT TUBS FULL OF WATER AND PEOPLE ARE VERY HEAVY!
Let's say you have an average weight of 165 for each of 8 people in a full, large hot tub. What's that?
500 x 8.33 = 4165
plus 1000 pounds
plus 8 x 165 = 1320
I get 6485 pounds! Wow, that's a ton of weight!
So to speak...
Scrambling under a deck, when I see various things merely resting on other things, and all the weight to boot, I get exercised!
Someone is asking for a problem!
Look above. A corner is resting on the middle of a column. And necessarily as those vent flaps kind of need to open.
And to the left, the exterior beam for the deck is resting on a built-up support (using interior, not galvanized, lag bolts which are rusting!) with another joist and the stairs merely nailed to that! This is haphazard at best, and that is not a good technique when so much weight is in the picture.
This is a very large hot tub and I am going to assume it's about 6000 pounds when full of people! Decks can be strong, but over time is the wood able to handle that dead, then live, load? Only the structure can determine that.
My recommendation: decks are always best supported by a patio on the earth. IF a deck is used, and they can be, it must be constructed such that it is capable of handling this load over time. When joists and under support is merely HAVING A REST on top of something else, and not securely attached, the results cannot be good.