같애 is common in spoken Korean but it's not proper in the formal sense.That is, it's not standard Korean. There are many examples like that. For example, if you wish or hope something, standard Korean is "바라(요)" but "바래(요)" is very common in informal or spoken Korean. Or when you express surprise, to be surprised is "놀라다" but it's quite common to use "놀래다" (the latter is actually causative and means "to surprise (someone)". So as an exclamation of being surprised, you can say "놀래라" (but "놀라라" would be grammatically correct for standard Korean). To avoid any confusion, this is different from what in phonetics is called "fronting." An example of this would be "맥히다" instead of "막히다" (= to be blocked or backed up). In a case like this, the preceding vowel is 'fronted' (this refers to the position of the tongue in the mouth when pronouncing the vowel) because the following vowel is 'i'. It's a kind of phonetic assimilation to ease pronunciation.

"같아" and "같애" are the same. But, "같애" is informal and isn't predominant. I suggest you not using this form in formal situation.