It is really not recommended as they do have a tendancy to put things in their mouths, like little human babies, more so than other rodent species such as rats. As well as pouching the fluffy fibres the threads which chewing produce can also get wrapped around limbs, especially young babies, and amputation is a serious consequence, even strangulation. Ingesting the fibres they can get trapped in their stomach/intestines causing blockages, which if caught quickly enough can often be treated but are more often potentially fatal.
Like most things
some hamsters are fine. Many hamsters have used the fluffy bedding you often see sold in petstores for years with no ill effects,
others have suffered terrible injuries and death. You should see a warning on fluffy bedding now indicating it is unsuitable for nursing mothers but really it should just be removed altogether as there are so many other alternatives.
For picture posing purposes it will generally be okay, just be vigilant as always, and similiarly if they show no interest in eating fabric then it is usually okay to let them play in a hammock etc. during play time, whilst they are under your constant supervison, just in case they change their mind, and just in case they get up to any other mischief
Like use it as a trampoline to bounce out of their playground
I would personally be wary of leaving a hammock etc in an enclosure overnight, I know some people do though with no problems but if something were to happen I would not be happy knowing I could have prevented it. Maybe if you were able to make a hammock from rice paper or vegetable fibre? I am not sure if such things already exist on the market? I have certainly never heard of any specifically for hamsters but it would be possible to manufacture something and they would definitely sell.