Is it permissible to use Islamic poetry, such as: "My Lord, I call upon You, and none but You do I call upon… Who else but You in this universe cares for me?" in supplication during the Witr prayer and prostration?

It is permissible to supplicate with that which contains no sin, aggression, or contradiction to creed. However, the best is to supplicate with the ma'thur (transmitted prayers) from the Prophets, because they were granted comprehensive words. The permissibility of supplicating with non-ma'thur prayers is indicated by the Prophet's approval of some companions' non-ma'thur supplications, and by the generality of the Hadith in Muslim: "The servant's supplication will be answered as long as he does not pray for a sin or the cutting off of kinship ties."