JR West 1 Day Pass

Is it true that the JR west pass (Kansai Wide Area) now include unlimited ride on Bullet Train "SANYO SHINKANSEN"?

http://www.jr-odekake.net/en/jwrp/kansai_wide.html

Can I buy a 1-day pass to travel from Kyoto to Arimaonsen?

Yes, it's true.

Arima onsen is not served by JR. You can go until the middle of the way with the pass, but need other transportation to reach Arima.

Thank you for the advice. I would like to get on the shinkansen. This is great.

You guys are confused by JR West Kansai Area Pass and Sanyo Area Pass.

You cannot ride any Shinkansen with the Kansai Area Pass. You'll need to get the Sanyo Area Pass if you want to ride the Shinkansen. There is NO Sanyo Area 1 dat pass:

http://www.westjr.co.jp/english/travel-information/pass/

3 types of passes
http://www.jr-odekake.net/en/jwrp/passes.html

You guys are confused by JR West Kansai Area Pass and Sanyo Area Pass.

No, you are the one getting confused now. The pass in question is the new JR West Kansai Wide Area Pass as explained here:-
http://www.japan-guide.com/e/e2361_08.html
And also shown in the link provided in the original question:-
http://www.jr-odekake.net/en/jwrp/kansai_wide.html

You cannot ride any Shinkansen with the Kansai Area Pass.

But you can ride the Sanyo Shinkansen with the Kansai Wide Area Pass (between Shin-Osaka and Okayama)

You'll need to get the Sanyo Area Pass if you want to ride the Shinkansen.

Or the Kansai Wide Area Pass as per above.

So, YYW can take the Sanyo Shinkansen from Shin-Osaka Station to Shin-Kobe Station, and then take the subway from there to Arima Onsen as explained here:-
http://www.japan-guide.com/e/e3558.html#jump_access

Obviously, to get full use out of the JR West Kansai Wide Area Pass you should also use it for day trips elsewhere (eg. Kinosaki Onsen, Okayama, Hikone, etc.)

If you can list your whole itinerary YYW we can advise if it will pay off or not.

Enjoy your trip!