No, they're different.
Another interesting thing they did was reconstruct the opening and closing credits. The font is slightly different, most noticeably the letter W. The Astroboy title no longer "zooms" onto the screen.
I think I got this bit wrong. I've checked the Siren version and the title card does zoom out from the viewer. The "©" symbol has a thin outline and appears below the R in ASTROBOY, and the copyright line disappears as the same time as the title when Astro flies through it. The "&" symbol in the opening credits is drawn with a single unbroken line. It might be the original English broadcast opening, but unfortunately I don't have a surviving copy of that to check.
The Madman DVD version is definitely a redone version. The title card is drawn with a laser beam, then moves up and closer. The "©" symbol has a more even weight and appears below the T in ASTROBOY, and the copyright line disappears before Astro even shows up. The "&" symbol in the opening credits has a broken line in the upper right curve.
While I'm at it, here's a few more versions:
The Manga VHS opening is the same as the Siren version.
The Japanese Bluray opening has the original Japanese title card, fonts and subtitles. Audio is English or Japanese.
The Manga DVD opening is the same as the Japanese Bluray, but with English audio only.
The AnimeLab streaming version is perhaps the most interesting. It's the 1080p Japanese Bluray "clean opening" version, so it has a Japanese title card but no other Japanese text for credits or subtitles. Below the Japanese title, is the English zoom-out title card like the original English TV broadcast. Below it is the copyright line, which looks and behaves like the original English broadcast version but with the "©" having an even weight. The opening credits are in English, and appear similar to the Madman DVD version. Audio is English only. Someone put some effort into this. IIRC, AnimeLab was Madman's streaming service. It was bought out by Funimation who immediately dropped the show from their lineup, so this version is not available anymore.