Does anyone know what kind of lossless coding DTS-HD Master Audio uses, i.e. does it use LPC, and if so, does it use FIR or IIR filter structures?

I'll answer that myself: the residual is formed by subtracting the decoded version of the lossy DTS signal from the uncompressed original bitstream, and the residual will just be entropy coded, because it'll look like white noise - like how MPEG-4 SLS works. A DTS-HD Master Audio signal consists of both the backward compatible DTS "core" signal and the lossless difference signal. Stand-alone lossless is supported, so there will probably be an LPC coder in a DTS-HD encoder, but lossles-only isn't likely to be used much.