This will not reduce time complexity, just space complexity; as well as spending less time in the interpreter, most of the work being done in C.

The key idea is to make use of generators to avoid building lists that you only iterate once; reducing your need for memory management, thus increasing the overall speed.

Since you are already importing itertools, I’ll just import the relevant parts to save on typing a bit, feel free to use the long names if you see fit:

from itertools import product, permutations

in case you are using Python 2, I'd use:

from itertools import products, permutations, imap as map

Now we transform each list into a generator expression:

def _compare_names_with_combinations(name_1,name_2):
    join = ' '.join
    name_1 = name_1.lower().split()
    name_2 = name_2.lower().split()
    distances = []
    for name1 in map(join, permutations(name_1)):
        for name2 in map(join, permutations(name_2)):
            distance = _compare_names(name1,name2)
            distances.append(distance)
    return max(distances)

Now product lets us merge the two loops:

def _compare_names_with_combinations(name_1,name_2):
    join = ' '.join
    name_1 = name_1.lower().split()
    name_2 = name_2.lower().split()
    distances = []
    for name1, name2 in product(map(join, permutations(name_1)), map(join, permutations(name_2))):
        distance = _compare_names(name1,name2)
        distances.append(distance)
    return max(distances)

An other improvement is to not build the list of all distances since we are only interested in the maximum value: let's put this max call out of the function and turn it into a generator:

def _compare_names_with_combinations(name_1,name_2):
    join = ' '.join
    name_1 = name_1.lower().split()
    name_2 = name_2.lower().split()
    for name1, name2 in product(map(join, permutations(name_1)), map(join, permutations(name_2))):
        yield _compare_names(name1,name2)

def score_names(name_1, name_2):
    return max(_compare_names_with_combinations(name_1, name_2))

Well, we’re just mapping _compare_names over the product. Maybe we could have that max call in the function after all:

def _compare_names_with_combinations(name_1, name_2):
    join = ' '.join
    name_1 = name_1.lower().split()
    name_2 = name_2.lower().split()
    return max(
        map(
            _compare_names,
            product(
                map(join, permutations(name_1)),
                map(join, permutations(name_2))
            )
        )
    )

But this will require that we modify _compare_names to accept a tuple of two names as parameter instead of two names as two separate parameters:

def _compare_names(names):
    a, b = names
    return SequenceMatcher(None, a, b).ratio()