But if the sentence doesn't have the verb 是in it, is it still correct to use 是不是 as a tag question? Example: 你认识我，是不是？
Yes, even if it is a nominal predicate sentence (without verb).
Besides, 是不是 can be placed at the beginning of the sentence, at the end of the sentence or between the subject and the predicate. So the following examples are all correct:
Example 1: 是不是你认识我？
Example 2: 你是不是认识我？
Example 3: 你认识我是不是？
The example sentence was: 您是李老师，是不是？
That is not wrong, but please note that in the case of a "是" sentence you can also say:
Generally speaking, "是不是" can be used to raise questions when the speaker wants to confirm what she already believes.