No, they are not used, even when people speak standard arabic.
It's not uncommon for news prodacstors and public speakers to omit these end-of-word vowels.
You should note that Arabic Dialects are technically (from a linguistic point of view) different languages with different grammar rules. Egyptian arabic has بتاع to mean "of", Iraqi uses مال to mean "of", Syrian uses تبع to mean the same thing.
But, these are optional, so the sentence:
باب البيت الصغير
Can still occur in dialects, the pronounciation will be radically different from standard arabic, for example:
Syrian: baab ilbeet liz ghiir
Egyptian: babil beet essughayar
Iraqi: baab ilbeet liz ghayir
The meaning is the same, and as you noticed it's ambiguous as it could have two meanings.
So how do we distinguish? We don't. It's ambiguous. Mostly the meaning is deduced from the context. If the listener/reader knows the house has small entrance, he will interpret it as such. If the listener knows you're talking about two houses, one of them being small, then he will interpret the sentence as such.
Of course it is possible to remove ambiguity by using the "of" construct, here's the example in Syrian:
The small door of the house:
الباب الصغير تبع البيت
The door of the small house
الباب تبع البيت الصغير
Hope this helps.
P.S. I just realized you used مدخل and I used باب in my answer. sorry :P too lazy to go back and fix them all.