Yes, like Emily already said Opera Mobile Classic is the way to go for normal user scripts.
But if you want some advanced GM_ functions to work like cross domain / cross site GM_xmlhttpRequest then your only option right now is:
Opera Mobile Labs (with Extensions) (link to
APK is on that site).
Install+run Opera Mobile Labs app and visit
Violent Monkey's extension
site and install the 1.5.1.1 (OEX version)
by clicking on "Add to Opera" and then choose "OK" (maybe you'll have to
restart Opera Mobile for the extension to work.).
To install an userscript you just need to load it in the browser by
visiting the user.js URL location. If you have userscripts on your SD
card, you can load them thru entering "file://" into the address bar and
navigate to your user.js files and then choose "OK".