Although Hidden Palace Zones mappings and sprites no longer exist (now uses OOZs sprite placements), it looks like the colision is still there in this version as well; and continues to stick around all way up until Sonic 2 Beta 8 where it's officially gone (the garbage around the stage looks different, much more like the final versions garbage). I can't verify for sure but the garbage shown in Sonic beta 5, 6 & 7s HPZ looks identical to the garbage shown in Sonic 2 beta 4.
I started adding this stuff to the wiki, let me know if I screwed up: http://info.sonicretro.org/Sonic_the_Hedgehog_2_Beta_5 Someone else will have to upload the pictures, since I'm a trial member.
Two minor finds: Find one: EDIT: Removed, as it's old news actually, but was posted in a different proto topic. Find two: In Oil Ocean 2 you know that place where people usually do the "Mega Sonic" bug? In this beta, these spikes AREN'T THERE. A major insult to Mega-Sonic fans. See for yourself. Beta: Where are the spikes? (image) Why these spikes aren't there?! Final: A soon-to-be Mega-Sonic says "Hello!" to the added spikes. (image) NOW we get a chance to do Mega-Sonic. What do you like more, Mega-Sonic or a chance to outrun the fatass Robotnik?