Alright, I'm pretty sure it is not.
sh in pinyin is a [ʂ] in IPA (http://en.wikipedia.org/wiki/Voiceless_retroflex_sibilant), while
sh in shampoo in English, is a [ʃ] in IPA (http://en.wikipedia.org/wiki/Voiceless_palato-alveolar_sibilant).
Although it sounds pretty close and as a near-native speaker of Mandarin Chinese I use the SH in shampoo to pronounce [sh] in pinyin. Still I don't think the listed entries in the wikipedia is correct on this one. (https://en.wikipedia.org/wiki/Template:Transcription_into_Chinese)
So what do you think? I'm near-native in Mandarin Chinese but no professional linguist.