It sounds as if you are using the debugger inside VIM (is there even an integration available?³), but I think you are calling vim from the debugger. (right?)

AFAIR in the latter case you are able to customize an editor inside the debugger to edit multiple lines², wouldn't surprise me if Mac doesn't like VIM.°

Or are you talking about switching only the line edit commands from GNU (i.e. emacs) to VI?

IIRC there is a set option to do so.

see http://vim.wikia.com/wiki/Use_vi_shortcuts_in_terminal

°) understandably as an emacser ;-)

²) seems what I remebered was the pager support, which doesn't really allow to edit the history though!

see

  DB<1> h |
|dbcmd        Run debugger command, piping DB::OUT to current pager.
||dbcmd        Same as |dbcmd but DB::OUT is temporarily select()ed as
+ well.
[download]

³) a sure Fritz Mehner of course :) http://www.vim.org/scripts/script.php?script_id=556