The Cloud T is not as flat as a carrycot, and it's still restrictive to baby's position - all car seats will be because they need to prevent the baby flying around in the event of a car accident. There's no "official" exception to the rule for these seats. I think the marketing is a bit misleading in that area. If you look on their FAQs they even say something vague about not leaving the baby in the car seat for long periods "for safety reasons".
BUT also, it's a guideline not a law - you can make your own judgement. The guidelines for time limits are not really based on seats that are designed like this. They are based more on seats which are less supportive and more upright. However having said this, fully reclined the "lie flat" seats such as Cloud T are still steeper than 10 degrees incline. The Fisher Price Rock n Play Sleeper was recalled in the US because it was found to be responsible for around 100 deaths (30 before the recall, 70 after). The Rock n Play has an incline of 30 degrees - the recommended maximum incline for sleep safety is 10 degrees.
Cybex Cloud T is somewhere between 10 and 30. The exact angle probably varies based on the angle of the adapters on the buggy. 30 degrees is more like the angle in a typical infant car seat without the "lie flat" feature. And the Rock n Play was especially problematic because it was marketed as a sleep space, meaning many people used it for unsupervised naps and/or overnight.
Carrycots are considered beneficial for two reasons - first you get that totally flat surface less than 10 degree incline which is considered safest for sleep and airway position. If it's not approved for overnight sleep this benefit doesn't go away, that is probably more due to airflow in the side panels, so it's OK for supervised sleep, when you're awake, but you should not let babies sleep in it and go to sleep yourself especially for hours. It also won't be that it's definitely UNsafe for sleep, but more that it doesn't have the correct certification.
The other benefit of the carrycot is that babies need some time every day outside of "containers" ie devices where they are held in a specific position and usually restrained using safety straps. They need time to lie flat on a surface like a cot, playpen or blanket on the floor, in order to develop their gross motor skills - rolling, sitting, pushing up etc. A car seat is counted as a container whereas a carrycot is classed as a flat surface.
I don't think you necessarily need a carrycot though - it just depends on how your pram works for the recline, and how much you intend to use the pram. A lot of the Cybex ones do have a seat unit which can be opened out completely flat which is what I looked for and used when my children were tiny. And then I just let them have plenty of time to roll around on the floor, our bed etc rather than keeping them strapped into things all the time.