Ever since I heard Shai Linn interviewed by Mark Dever I have regarded him as a brother in the Lord who is pious and intelligent, one who thinks deeply about ministry, words, and the Word. For such a young man he has demonstrated a maturity that is not often found in twenty-somethings.
So what about “hottest” as an adjective or appellation for God the Father? I do not believe that God was blasphemed in the lyrics under question. In Longman’s Dictionary of Contemporary English there are more than a dozen entries. The two most relevant would seem to be the two below:
Longman Dictionary of Contemporary English
3 very popular/fashionable
informal something or someone that is hot is very popular or fashionable, and everyone wants to use them, see them, buy them etc:
one of the hottest young directors in Hollywood
Michael Owen is already one of soccer's hottest properties (=actors or sports players who are very popular).
The movie is going to be this summer's hot ticket (=an event that is very popular or fashionable, and that everyone wants to go and see).
be the hottest thing since (sliced bread) (=used about someone or something that is very good and popular, so that everyone wants them)
Her new book is supposed to be the hottest thing since Harry Potter.
4informal very good, especially in a way that is exciting:
• a hot young guitar player
• a hot piece of software
• His new film is hot stuff (=very good).
be hot at doing something
• She's pretty hot at swimming too.
not so hot/not very hot informal (=not very good)
• Some of the tracks on the record are great, but others are not so hot.
be hot s*** American English informal not polite (=used about someone or something that people think is very good)
hot - Definition from Longman English Dictionary Online
Now while the appellation “hottest”, in reference to God, would not be blasphemous it leaves open the question of whether or not it would be wise to use it in this way.
Given the target audience, (21st century, English speaking, young and technologically connected people) it could be argued that less than desirable connotations will be in the foreground of the listener’s vocabulary. Here we might have an occasion of causing unnecessary offense or laying a stumbling block in our brother’s way. I will leave it for others to work through that one on their own.