Simple answer: yes, the purchase of a computer is a qualified expense for a 529 plan distribution.
There appear to be two issues in your question:
1. Does dual credit courses count? That question is academic starting in 2018, as 529 distributions can be used for qualifying expenses for K-12.
2. Are computers a qualifying expenses? The rules are loser for 529 plans than the education credits. Computers must be required by the college for the credits. You'll find no such restrictive wording under qualified expenses for 529 plans.
Just do it.
