The only caveat to be aware of is if Pentax creates additional information in relation to the DNG. For example, there was a drone camera, created by Hassleblad, that produced DNG that had problems being imported into LrC until it was formally supported. They had a secondary set of information. I'm not saying you will have a similar problem but just be aware.
The difference lies in the word Proprietary. I used to shoot with a Pentax. I always shot with the camera set to shoot DNG. DNG is a public universal format. The information fields in the DNG file header block are described and documented by Adobe (the developer of the file format) and made public for anyone to use. The data block for a RAW file contains values recorded at the Photosites on the sensor. RAW photo sited are not converted to RGB pixels. The PEF file format is like the DNG RAW file format in that it has a Header block and a RAW data block. So either file format contains the same photo site values in the data block. The difference between the two file formats is the information fields in the header block are not described and documented by Pentax and can only be read and interpreted by PENTAX image processing software. Eventually Adobe and other image processing software developers will reverse engineer the proprietary PEF file format and be able to process the PEF RAW file data.
