In the newest Atkins book (A New You) caffeine is allowed. The science changes all the time and whilst it is not advised to guzzle caffeine-containing drinks I feel sure a few cups of tea a day won't hurt! I use decaf coffee, tho, after 12 noon each day as I am a bad sleeper. Some days I only have decaf coffee. But I don't like decaf tea - would rather have one or two cups of regular tea than double the amount of decaf!
If you are not seeing any problems, like stalling or increased appetite or whatever, then I'd say you are fine with your tea x