Hello! I am not a native Japanese speaker but since I thought your question is interesting I looked for the explanation myself.
It is correct to use both を and に but the sentence would have to change according to what you use.
When you use を, you emphasize respect towards the person you are visiting.
On the other side, when you use に, you emphasize respect towards the person that is visiting, the subject of the sentence.
In other words, yes, your sentence is correct. However, if you were to use に, you couldn't be talking about your own person as it would sound like "the almighty myself is paying a visit".
Also, paying such respect towards X san, the one visiting (when using に) would also mean you'd have to replace ～する with ～なさる to mantain the politeness.
If you still want to use に about your own person, you could replace the verb with 伺う.
This is the best explanation I found here: http://detail.chiebukuro.yahoo.co.jp/qa/question_detail/q1421122654
I hope this was helpful (w)/
訪問するの使い方。。。
I was wondering which particle to use for the following sentence (or, if this is an awkward way to say it).
I visited my grandmother over winter break.
冬休みにおばあちゃんをほうもんした。