Can we use same IP address for Virtual server and Same IP on SNAT pool?

Yes, you can. SNATPOOL is used for egress traffic, so here it will be your VS address going as outbound traffic.

You can read through the doc's for more understanding. It all depends on the infra and how one would like to use it. Some use self-ip's, some use a pool of ip's & some prefer the same VS address as the snat address.

Yes, there's nothing stopping you using this configuration. I've seen it done at one place I've worked at before.

Any reason why you need to do this? If you need to try to identify the source of the connection on your servers, you can use XFF headers if the traffic is HTTP.