Yes it's okay to sleep in a messy diaper and it feels great.
If I need to poop before bed I will just poop in the diaper and then go to sleep in the messy diaper and then change later on in the day.
Diapers that are messy as well as wet are a great feeling and I find that I sleep better when I sleep in a wet and/or messy diaper.
I love to walk around in the day as well with a messy diaper and a wet diaper.
The squishy feeling of the wet diaper in between my legs is a great feeling.
I wear diapers all the time now and no longer use the toilet so I always have at least a wet diaper on and I also poop the diaper in public and then change when I get home.
I also have worn a messy diaper as well as a wet diaper all day before.