When you say the centre of the page do you mean right in the centre (such as a watermark might be)? Otherwise Fellsider's suggestion will put it in the centre, but at the foot of the page.
What I think you are actually after is a watermark (such as "Draft" or "Private & Confidential", which might appear on a report, for example. As to how to do it - I'm not sure so just going to go and have a play around!
I suspect not because from reading the links above what it has done has in effect put an "object" over the relevant cells. The fact that you can read the figures is because you have made the "object" i.e the word art, semi-transparent. However, this has the effect of blocking the cells.
Another option may be to set up the watermark in the printer properties, as most printer s/ware will have this option. However this may not be a feasible alternative if you want "Page N" as the watermark on the relevant page.