First, there's the problem that you're passing non-existent variables $HoA1 and $HoA2 to the sub. (Yay for using use strict;!)

You want to pass the hashes, but you can't do that. You can only pass scalars as arguments. So let's pass a reference to the hash instead.

test(\%HoA1, \%HoA2, ...);
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Then there's the problem that

test(\%HoA1, \%HoA2, @a, "test");
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is the same thing as

test(\%HoA1, \%HoA2, "entry1", "entry2", "entry3", "test");
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When you do

my ($HoA1,$HoA2,@a,$test) = @_;
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there no way for Perl to know how many of the remaining args go in @a, so they all go into @a.

Just like with the hashes, you'll need to pass a reference to the array, not the contents of the array.

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All together, we have:

#!/usr/bin/perl

use strict;
use warnings;

use Data::Dumper;

sub test {
    my ($HoA1, $HoA2, $a, $test) = @_;
    push(@{$HoA1->{"HOA-1"}}, "Entry Two");
    push(@{$HoA2->{"HOA-2"}}, "Entry Two");
    print "Array: @$a\n";
    print "Test:  $test\n";
}


my %HoA1;
my %HoA2;

push(@{$HoA1{"HOA-1"}}, "Entry One");
push(@{$HoA2{"HOA-2"}}, "Entry One");

my @a = qw(entry1 entry2 entry3);

test(\%HoA1, \%HoA2, \@a, "test");

print Dumper(\%HoA1);
print Dumper(\%HoA2);
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Note that I removed the return value since it's not needed. Since you're modifying the caller's hash through the reference, the caller already sees the changes being made by the sub.

Tip: Dumper's argument is a scalar. Don't pass a hash. If you want to dump a hash or array, pass a reference to it. It'll be much easier to read.

Update: Missed the first problem originally. Added the bit addressing it.