One Linux-based HPC vendor bought out another Linux-based HPC vendor, this will not really effect Linux on HPC. All of the Top 10 of the TOP500 use Linux in one way or another. The Blue Genes have SLES on the service nodes and CNK on the compute nodes. The SGI is SLES with add-ons. The HPs are Linux clusters. The Crays are SLES on the service nodes and either Catamount or Linux on the computes.
Linux is very pervasive in HPC and becoming more so. Since I know a little something about Cray, the newest vector and scalar lines both use Cray Linux Environment (CLE) formerly called Compute Node Linux (CNL). Cray's CNL was released in second half of 2007 and already over half of the Cray processors in production are running CLE on the computes instead of Catamount, the very lean, proprietary compute node OS.