Using the wp_remote_post response body

Your question doesn’t make a lot of sense.

The submission works but I get the returned URL as an HTML stream in
$response['body'] but I cannot seem to get any query string values
from it.

That is what is supposed to happen. You requesting a web page just as when you click a link in a web browser, except programatically.

Again…

Is there a way I can capture the actual URL value with query string
that they send, rather than this being interpreted as an HTML stream?

… doesn’t make a lot of sense. You are requesting a web page. “They” are not sending an “URL value with query string”. You are sending one and a server is responding. As you are requesting a web page, what you get is a web page. However the body of the page is not the only thing returned. Check the Codex:

Array
(
    [headers] => Array
        (
            [date] => Thu, 30 Sep 2010 15:16:36 GMT
            [server] => Apache
            [x-powered-by] => PHP/5.3.3
            [x-server] => 10.90.6.243
            [expires] => Thu, 30 Sep 2010 03:16:36 GMT
            [cache-control] => Array
                (
                    [0] => no-store, no-cache, must-revalidate
                    [1] => post-check=0, pre-check=0
                )

            [vary] => Accept-Encoding
            [content-length] => 1641
            [connection] => close
            [content-type] => application/php
        )
    [body] => <html>This is a website!</html>
    [response] => Array
        (
            [code] => 200
            [message] => OK
        )

    [cookies] => Array
        (
        )

)

Perhaps what you are looking for is in the headers.

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