In this discussion, it seems that Codechef replies to problem setting emails within a few hours, and someone mentioned that they will not email you if your problem was rejected.
I sent some problem proposals last month ago already, and have not received an email back from Codechef.
Is it safe to assume that my problem has been rejected?
I’m still allowed to use the problem ideas in other contests/sites then?
Is it in bad taste to resubmit them to CodeChef again?
Not always - I have had responses in a few hours, but others have taken weeks. CHGORAM2, for example, took 22 days to get a reply. My most recent one was submitted on 10th February, with no reply yet.