Although the Pomegranate is not toxic as such, it does contain quite a high level of tannins which can inhibit the absorption of iron if too much is ingested, and can also give a bitter flavour that might not be enjoyed by some tortoises. The calcium/phosphorous ratio is poor too, so this is not a plant that we would recommend feeding, although the occasional nibble would do no great harm.
Never feed the fruit of the Pomegranate unless your tortoise is a fruit-eating species, and even then feeding should be limited because of the number of seeds contained in the fruit.
In the UK the Pomegranate can be grown outside in most areas for its foliage and the flowers which range in colour from red to a very deep orange. See also Pomegranate (Fruit).