[eluser]smilie[/eluser]
In short - yes, you can do that.
What I have learned (by accident, but never the less) is that all queries between start and end of transaction are dealt by DB transaction system. It does not matter _where_ queries are, for as long as they are inside transaction start / end.
This means, that you can start transaction in controller, then execute queries in models, helpers, libraries - where ever - for as long as they are called inside start / end of transaction.
Have fun!
Cheers,
Smilie