The shops in Subic might tend to be a little more diligent than in other places in the Phils, so proof of certification would certainly be a requirement for diving there.
A c-card, by itself, is adequate to prove your certification and go fun diving. If you are PADI trained, then the PADI affiliated dive centers (Johan's and Arizona) will also be able to confirm your qualifications via the PADI online database. Blue Rock is SSI - and may have similar capability for that agency. Boardwalk is SDI for their recreational training - not sure if SDI have an online database for their certifications.
Displaying a log-book isn't mandatory, and not having one certainly won't deny you diving. However, you won't have proof of experience, which could mean that initial dives are 'easier' until the dive center/divemaster get to know your capabilities.
There are two main areas where expats live in Subic Bay (I've lived in both):
Binictican Heights is in the hills overlooking Subic Bay from the south. It's a 10 minute drive down to the Bay itself from there. The area is quiet and surrounded by jungle. It's popular because the housing is former Officers' quarters from the days of the US Navy base.
Baloy and Barretto beach areas is also popular with expats. Right on the beach and economical value. Plenty of residential accommodation around there - so that sounds likely, from your description. Houses run from those areas down the main highway/beach to Subic Town proper.
There isn't much residential accommodation in the main SBMA/SBFZ area, so it's unlikely he lives there, unless he stays in one of the 'executive condo' buildings. There are a few houses around the fringes of the bay, more remote and expensive.
Some expats choose to live in Olongapo town proper - that'd hardly be described as 'by the beach'.
. I think it only happened to me once in Bohol when I booked a dive to Balicasag.
