No native linux client and from what I've read on here, there isn't likely to be one soon. I'm not a gui programmer, but I do think the fact that there is an MAC OS X client would imply that they should be able to do it when there is enough demand.
This redbook talks about installing R6 under Crossover...
http://publib-b.boulder.ibm.com/Redbooks.nsf/RedpieceAbstracts/sg246835.html?Open