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By casting this spell, you request your deity to send you an outsider (of 6 HD or less) [b]of the deity's choice[/b+. If you serve no particular deity, the spell is a general plea answered by a creature sharing your philosophical alignment. If you know an individual creature's name, you may request that individual by speaking the name during the spell (though you might get a different creature anyway).
RAW the scroll contains the spell, not the version cast by a cleric of a specific faith, so you would have access to the planar allies allowed by the deity of the person casting the scroll.
The result is not random but is your deity that decides what you get. If you don't serve a particular deity you get something appropriate for your alignment. Generally, you get a creature with the maximum number of HD possible, but what you get can depend on how faithful to your deity or alignment you have been, and what creatures serve your alignment or deity.
With all the books that have been printed, I doubt there is any deity or alignment that hadn't a 6 HD servant that you can summon.
I would allow a Knowledge Religion check to recall the name of a specific servant of your deity. Probably with a DC of 20.
Personally, in a home game, I would make the scroll a scroll of Lesser Planar Ally - Lamashtu, and have Lamashtu choose what you get.
Anyone with the spell in his spell list would automatically notice that it is keyed to a specific deity. People trying to activate it with Use Magic Device will have to decipher it before trying to use it to notice that.