I have done some research on this and here is the apple developer page on there dynamic loader for OS X. Here is the page on dlopen. It appears you can use this on either dynamic libraries or bundles with dlopen. So you should just be able load the bundles with the properly specified mode.
Plugin code-loading should be OK, for versions before Mac OS X 10.4 there is
dlcompat -
Apple only mention the latest and greatest stuff as usual (where dlopen is new for Tiger)
AngelScript needs a few more calling conventions for Darwin (ppc/x86),
as not all the plugins use GENERIC ? (at least that is how I understand it)