No, many stories, like The Power of the Daleks or Daleks in Manhatten indicate the Kaled mutant can be grown in a lab like environment, given the right materials. Add to that a specifically created Scientist Dalek and it shouldn't be too hard. The Progenitor from Victory of the Daleks clearly was designed like a 'seed ship' of sorts that creates Daleks specific for the needs of making a new colony. Interesting notion, they could've salvaged what they could from past adventures and kept the sane ones and put the rest in the Asylum in a bid to nurse them back to health. Clearly the size of the population grew too much to handle/stability of the population was deemed to irrelevant to fix and was thus sealed off. It's possible they raided past Dalek losses in a bid to gain raw materials for creating their new army and the Asylum became a bi-product. OR during the Time War the Daleks were scooped up from all time zones and those that couldn't fight were dumped in there.