I met a similar problem recently, and I think the batches should be the same across different GPUs according to the source code.
If you look at the function DistributedSampler which we use in DDP,  the chunking function is done by this class. However, if you look at the source code of Dataloader, sampler will not affect the behavior of data fetching of iterable datasets.
see line 34 in https://github.com/pytorch/pytorch/blob/8fd9fe93be08c9f0ab81507081fac1387a4aca56/torch/utils/data/_utils/fetch.py#L18 72