I am travelling to Rome in late May, the flight does not get into Rome until 9pm local time.

My hotel is approx 1 km from Termini station, any advice on if I should take a taxi this late, or will I still be ok to ride the train to Termini then cab it from there ?

Last train to Termini (Leonardo Express) is at 11:37 PM so you should be able to make it.

Are cabs easy to get at Termini??

Cabs are everyplace outside Termini. You shouldn't have any problems.

Yes, there is a taxi stand out front. Make sure to go the official taxi stand where you will see a line of taxis waiting. Do not go with anyone that approaches you in the terminal or as you walk out to the taxi stand. There are plenty of scam artists working the terminal. Also look out for the guys that insist on helping you load your luggage into the taxi and then demand two Euros in payment.

Thank you all for your tips

I'll be especially careful to make sure I load my own luggage into the cab