JapanNewbie

I tried looking it up in a Chinese dictionary, and it didn’t come up (although that doesn’t necessarily mean the word doesn’t exist). But FYI, 胡 is defined as “recklessly, foolishly; wildly.” That could be related to being shady or doubtful? Here are some relevant 胡 examples (ok, ok, so Chinese is a different language, but still):

胡來 胡来 hú lái (v) make a complete hash of things; cause trouble
胡說八道 胡说八道 hú shuō bā dào (adj) babbling; (n) nonsense; blather; guff; waffle; (vi) blather; haver
胡思亂想 胡思乱想 hú sī luàn xiǎng imaginings; let one’s imagine run away with one

Um… えびす is one of the 名乗り readings for 胡, used only in names. If えびす can mean skin hanging from an animal’s neck, that’s very interesting, but I don’t think it has anything to do with 胡. Heather is right about 胡 having a connotation of “foreign” (eg. 胡座をかく, to sit cross-legged or “Indian style”), but even the Japanese aren’t sure how “scatter” fits in.
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One site speculating on the etymology tells the very colorful story of how, in 16th century Persia, there was a substance scattered on food like a spice which caused a drug-like effect similar to drinking alcohol. It was nice in small doses, but some people (of course) abused it, and this turned into a huge social issue. Thus, if someone smelled strongly of this substance, they were considered a suspicious person. The Japanese apparently agreed that smelly drug abusers were no good, so they coined this word just for them. Two other theories, given considerably less attention but sounding more likely, are that it had something to do with doubts about the Portuguese whom Japan was trading with, or that it belongs to the history of the Warring States Period.
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In other words, no one has the slightest clue how it came about. ^_^

This post has a pretty good research into the origin of “胡散”.

http://gogen-allguide.com/u/usankusai.html

After going through several possible explanations, including a kind of tea cup, the site believe it was a Japanese-made kanji compound, since the “u” is a Tang Dynasty sound while the “san” is a Han Dynasty pronunciation. That kinda make sense to me.

However, although the article found it dubious, I thought that the Chinese medical term made sense. “San” is a term for a powdery oral medicine. A very popular throat medication in Japan is still called “Ryukakusan” (San made from dragon horn), since it was based on a Chinese formula. Combine “胡”‘s most popular definition which is “foreign”, the term 胡散 literally means “foreign medicine”, which of course in terms of a sino-centric world is by default suspicious.

胡 in fact is the last name of many, many Chinese of Central-Asian or Turkish decent. When they decide to stay in China they usually have to pick a Chinese last name. Many of them choose “胡” to denote their foreign origin. If you know a Chinese friend with that last name, chances are his ancestors were not Han Chinese.