Are they the same?
Not exactly, I think Blu-ray PCM audio is specifically designed for multichannel audio with certain sampling rates. That means, there are multiple PCM audio streams laid out according to the Blu-ray audio format specification.
But still, it's in essence just PCM audio, so it is losslessly stored.
If not, how to extract Blu-ray audio without any conversion?
If your input is labeled as pcm_bluray, you can try copying it to the output with -c:a copy. But I'm not sure if this will work.
Conversion to a "normal" PCM format like -c:a pcm_s16le should always work, though, and it'd introduce no audible loss. The only thing that may be changed in such a case is the bit depth (e.g. from 32 Bit to 16 Bit).