Prolog and iOS : it would be OK

slidetocode.com offers
 - Raskell : basically a port of Hugs to the iPad (Haskell)
 - Lisping : originally a vi-ish editor for Scheme and Clojure
   but now includes TinyScheme interpreter, and the author is
   thinking of adding a Clojure (subset) interpreter.

Dmitry Kovba http://www.dmitry-kovba.com
offers an amazing bunch of "XYZZY Programming Language" apps
which actually do compilation and running remotely, which
neatly sidesteps any problems with adding new code to an iOS app.

Pharo Smalltalk runs on the iPad.  See
http://www.pharo-project.org/about/screenshots
As I understand it, the bytecode system is OK,
but the JIT would not be allowed even if it did
work for ARM.

Quicksilver Smalltalk sits on top of Javascript so it
can run in Safari, for example.  There is also something
called U8 (u8.smalltalking.net) which I've had little
luck learning about.

Pythonista http://omz-software.com/pythonista/
provides a Python IDE on iOS.  It's in the App Store.

So there is ample precedent for interpreted/emulated
languages on iOS devices.  SWI Prolog should fit right in.