babark: Yes, it is allowed. Humble Bundle specifically has infrastructure to handle this (you are able to "gift" steam keys).
I had noticed that, though I hadn't been aware of any specific rules regarding the gifting of keys. Thank you kindly for the clarification.
Hrm, follow-up question. If I recall correctly, the gift link thing was introduced some time between bundles 9 and 10. So for 10, I have the little gift boxes next to unredeemed keys. For 9 I don't, I assume clicking the Steam button doesn't automatically stuff games into my linked Steam account but still shows the key which I could then give to someone else - that fine, too? Or am I missing something again?