Yeah she's like a manifestation or some shiz Cloud and Aerith aren't and they are included in the couples montage in the credits - not the original KH one with other characters but the actual couples one in 2.856789 or whatever
Yes Tifa is included, they both are.
Squall sees her and speaks to her when she goes around Ansem's study looking for Cloud.
Not that it really much matters to the larger points on the table.
But while Cloud may not be literally romantically tied to this "light" there is a thematic parallel which is being relayed here, especially in light of AC being used as inspiration for their characters KH2. The person closest to Cloud's heart, his literal light in the darkness that is aiding him conquering said darkness, is Tifa. That's a very telling role to have Tifa fit in.
KH Tifa belongs there as much as KH Sephiroth as much as FFVII Aerith as much as FFVII Sephiroth.