php count с условием

Да, это возможно, конечно:

foreach ($offers as $offer) {
    $userCount = 0;
    $userBlistCount = 0;
    foreach ($offer->users as $user) {
        $userCount++;
        if ($user["mybl"] == 0 && $user["blist"] == 0) {
            $userBlistCount++;
        }
    }
    echo '$userCount = ', $userCount, "<br>", '$userBlistCount = ', $userBlistCount, "<br>";
}

Более красивое решение через count(array_filter(...