Well the Sony PVRs certainly use the MHEG version. The original BBC Blog about it stated that they were the main reason it was developed in the first place.
Anyhow, does it matter whether they are 'Custom' of 'Official MHEG' versions if they just work?
The list of Freeview HD devices with BBC iPlayer is actually quite big:
• 3VIEW Freeview HD PVR
• ADB i-CAN Freeview HD receiver and PVR: 2851T; i-CAN 5821T
• DIGITAL STREAM IP Set Top Box: DPS-1000
• HUMAX Freeview HD Receivers and PVRs: HDR-FOXT2
• LG Smart TVs: LV550T, LW550T, LW650T, LW950T, PZ570, PZ950; BluRay player: BD670 , HR600, HR650, HLX56S, HX46R, HX806 , HX906, HX966, HX976, HX996TS
• PANASONIC 2011 Viera TVs: VT30B, GT30B, ST30B, UT30B, G30B, S30B, DT30B, E30B
• Philips BluRay Player: BDP5200/05.
• SAMSUNG Smart TVs: C750, C650, C6500, C7000, C8000, C9000, D8000;
• SONY Televisions with Bravia Internet Video; Sony Blu-Ray Disk Players and Home Cinema Systems with Internet TV: BDP-S185, BDP-S280, BDP-S370, BDP-S380, BDP-S383, BDP-S470, BDP-S480, BDP-S570, BDP-S580; BDP-S770, BDP-S780; BDV-E280, BDV-E370, BDV-E380, BDV-E670W, BDV-E780W, BDV-E870, BDV-E980W, BDV-E880, BDV-EF200, BDV-F500, BDV-F700, BDV-H7000W, BDV-L600, BDV-L800, BDV-IZ1000; Sony Netbox: SMP-N100; Sony Freeview HD PVR: SVR-HDT500, SVR-HDT1000
• TOSHIBA Internet TVs: Regza RL Series, Regza WL Series, Regza VL Series