Yes, katakana is used only for loan words and such. Hiragana is used when they need to write particles and conjugations and all the grammatical aspects of japanese, since they don't use kanji for that stuff.
Blair would be written as ブレイア (bu-re-i-a), I believe. Either that, or ブレヤ (bu-re-ya), but I really doubt they'd use that. Of course, you can mix in the odd word in english letters when necessary in japanese. It's pretty common to see the odd phrase or word in english if it's a proper noun, or has some significance that would be lost in translation (some things just don't translate well.)