There's an article on eHow that you may find helpful.

Here is a link that might be useful: How to propagate a crabapple tree

Most malus are propagated by budding or grafting, not by own-root cuttings. There are a number of reasons for this. One of the most important is starting with a climate adapted and disease free root stock. Even if this particular variety could be rooted from cuttings, there would be a great deal more involved than sticking them in the ground in a sheltered place. There would also be no guarantee that the own-roots would result in a viable plant, let alone one with oomph.

The offer from the nusery seems very good, especially if they will hold them until they're sure the graft union has taken. If you had them graft several, there would be a margin for error. The owner would have to care for the potted grafts until they are large enough to plant out, but that should not present too many difficulties.

If there should happen to be another malus on the property, it would be possible to top graft scions from the desired variety onto it as another preservation option.

Hi,
thanks for your answers. It seems that suckers work mainly for plain species crab apples. By chance last Friday my boss and me made a dash to a nursery nearby to choose/ hand pick some trees. A nursery guy took us in a car to those plantings, and on the way I jumped on this chance and asked the guy exactly this question.
Without any hesitation he mumbled something like: grafting a bud, cuttings won`t work, stuff is always grafted, done in winter, then replanted.

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so I come back to the firs nursery`s offer. As long as the garden owners pay attention and put some TLC into those very young grafted shrubs they should develop and grow into healthy plants.

Well, always learning, thanks again, bye, Lin