Weetabix is not just made of wheat it also contains additives including sugar. Sugar when added to the gut if there is any evidence of fermentation occuring will increase the amount of gas in the gut resulting in an instantateous bloat, which can lead to stasis.
I would not advise giving any sugary products or processed foods to any animals.
If you want to give treats there are many natural products which are far healthier for them and just as enjoyable.