"Evidence" is anything that supports a premise. An IP address or profile is "evidence" as is an eye witness and DNA evidence.
Yes and no. You've listed 3 types of evidence with varying degree's of accuracy.
DNA is the most accurate, with dependencies mostly occurring in attempts to tell twins apart from one another.
An eye witness is good but the memory of an event starts to deteriorate over time and even initial accounts can vary from witness to witness.
IP address evidence is the least accurate. I can't disguise my DNA and if someone sees me steal a car they will at least be able to identify me as a Caucasian male. An IP address just tracks the culperate to the residence, it doesn't not account for people cracking WEPs and accessing networks that are not theirs or friends you may have given access to your network. Both of these examples don't track down the actual culprit. Just a residence.