I have let our Syrians out in the back garden (and will do again on suitable evenings this summer) after taking advice from Souffle and Pophammy who have done so with theirs. I chose a really warm evening, made sure they weren't in direct sunlight and used a rabbit run with small mesh for them to run in individually. I stayed with them all the time to make sure they were safe and didn't let them run free.
They all had a whale of a time and, after initially seeming a bit bewildered, seemed to realy enjoy sniffing round the run and nibbling dandelion leaves
I think it's important to understand the dangers - I know, for example, that there have been no pesticides or herbicides used on my garden for over four years.
I'm not sure about dwarf hams though - I haven't taken out Winter Whites outside and I'm not sure I will - they just seem so small and fast compared to our Syrians.