No the inner wall guards are fully aware because a) everybody who is stationed as a guard would have to go through the academy and 3D maneuver gear is pretty much part of the curriculum and b) if you recall from Annie's chapter it seems 3D maneuver gear is only to be worn in case there is a certain threat level to what they are called upon to handle (that time it was supposedly escorting Eren). Only guys who'd most likely be ignorant of the gear but lived within the wall would have to be really elite citizens protected in a bubble of their social circle, in that case its highly unlikely they'd be interested or involved in the truth. Even then the gear is of no particular importance for the truth. The ape man titan is still most likely an outsider because he's clearly ignorant of what is quite basic gear for anybody to identify if they lived within the wall. He simply took the gear with curiosity at what insiders had developed not out of some retrieval mission, they appear to have seen the gear before but looks like never managed to take it back in tact.
Well this chapter pretty much confirmed that the Ymir from the side chapter is most likely the same Ymir we see in the scouting legion, what is interesting though is why would Castle Utgarde be known by Hanji and moreover why would a castle located remotely have provisions that are most likely reserved for people who seem to be in the know (after all why should there be a canned good written in a language that clearly seems alien to commoners like Ryner). Its just weird to have food packaged from a community with a language that's not known to many, most likely indicating that language comes from outside the norm, be in a stronghold? What this indicates is at worst case scenario the outsiders, or whoever uses that language, has infiltrated the wall. Still I wonder why Hanji seems to be aware of the existence of the castle.
Another odd thing is... In the side chapter of Isle the titan affixed -sama to Ymir's name I'm wondering whether that titan was one borne inside the wall or outside. Because currently there does appear to be a faction borne outside the wall and the ape man appears to belong there given that why would the outside faction, if indeed that titan from the side chapter is one borne from outside, hold in high esteem the insiders? Lotsa questions are just piling up I hope the authors answers some of them soon. Well long as Ymir is there I'm sure we'll be in for a revelation soon.