Does this treat a successful run as though it was on HQ for game purposes, or does it turn the run into an HQ run to where they look at a card in my hand?

If successful they would get the reward for a successful run on HQ instead of the archives. So they would access one random card in your HQ (hand). The run itself is made on the archives, only the reward for success changes over to HQ.

They would access your hand and Gabriel would get his 2 credit (if he didn't get them earlier in the turn).

Could you clarify what card you are talking about?

Sneakdoor Beta (as named in the title), with text "[Click]: Make a run on Archives. If successful, instead treat it as a successful run on HQ."

All things that trigger from a successful run on HQ would trigger:

1) This was a successful run on HQ, Gabriel Santiago would gain 2 credits

2) HQ is a central server, everything that triggers off of a successful central server run would trigger (like Data Sucker)

3) This was a successful run, Desperado would trigger

4) Runner must access in the order of their choosing, the following cards, fully resolving each Access in order:

4a) Any upgrades present in the HQ server

4b) A single random card from the Corp's hand (HQ)

byronczimmer said:

Only for the first time each turn. If you succeeded at a Sneakdoor Beta run or a plain HQ run earlier in the turn, Gabriel already took his credits and wouldn't get them again.