'?' is used in Scintilla autocompletion as the default separator 
between a name and the number of the icon to display next to it. There 
is no SciTE setting to change this but a Lua script can set the 
editor.AutoCTypeSeparator property:

function OnOpen(f)
     editor.AutoCTypeSeparator=string.byte("~")
end

    calltip.<lexer>.word.characters controls which characters are 
considered part of identifiers for the purpose of calltip look up. It 
may be reasonable to specify

calltip.ruby.word.characters=$(chars.alpha)_?!

    More information at
http://scintilla.sourceforge.net/SciTEDoc.html

    Neil