Based on my reading on this topic, it appears that the separation between Tyromyces and Oligoporus is quite justified in terms of both molecular phylogeny and ecophysiology. Tyromyces, which pretty is pretty much restricted to Tyromyces chioneus (and perhaps some close allies), is a white rot fungus that is phylogenetically distant from Oligoporus/Postia/Spongiporus/Rhodonia/etc, which are all brown rotters and well ensconced in a brown rotter clade.

Sources:
Yao YJ, Pegler DN, Chase MW. 1999. Application of ITS (nrDNA) sequences in the phylogenetic study of Tyromyces s.l. Mycological Research 103:219–229.
abstract: http://journals.cambridge.org/...

Hibbet DS, Donoghue MJ. 2001. Analysis of character correlations among wood decay mechanisms, mating systems, and substrate ranges in Homobasidiomycetes. Systematic Biology 50:215–242.
http://tinyurl.com/homobasid

Link to original publication of name:

http://books.google.com/...