Can stem cells be clonned?

There are: Lots of different "stem cells." there is work in this area on embryonic stem cells. We do not have this technology for clinical applications, and certainly not in the hematopoietic arena.

Yes: Stem cells are remarkable in their ability to expand in a clonal fashion. Expand them long enough and you get one clone dominating. This is done in commercial and research labs all the time. Clinically this is done in very limited circumstances in the USA due to FDA regulations or guidance. My view is that a mixture of stem cells is better anyway, as clones, even if a lot, are suboptimal effect.