The LaTeX exporter does not honor the setting of
org-list-allow-alphabetical.  It exports ordered alphabetical list as
standard enumerate environment with numbered items.

org-mode 8.0.3

I placed the setq before loading ox-latex.  I read in the docstring that
org-list-allow-alphabetical should be set before org.el is loaded.  I
installed org-plus-contrib from ELPA and thus do not manually load org.el.

I found a post on this ml [1] on a related issue where the OP states that
doing the setq before loading the exporter solved his issue.

[1] https://lists.gnu.org/archive/html/emacs-orgmode/2013-04/msg01843.html