Is 'grep -v -l' equivalent to 'grep -L'?

No, they're not equivalent and as such the results will almost always¹ be different.
Let's see what each of those switches does:

‘-L’ ‘--files-without-match’ Suppress normal output; instead print the name of each input file from which no output would normally have been printed. 

This should be simple:
grep -L 'pattern' ./*
prints the name of each file that does not contain any line matching 'pattern'.

‘-v’ ‘--invert-match’ Invert the sense of matching, to select non-matching lines. 

This should be very simple too:
grep -v 'pattern' ./*
prints all lines not matching 'pattern' from each file.

‘-l’ ‘--files-with-matches’ Suppress normal output; instead print the name of each input file from which output would normally have been printed. 

Again, simple:
grep -l 'pattern' ./*
prints the name of each file that contains at least one line matching 'pattern'.

Now, what happens when combining -v and -l ? It's not much different from grep -l, except that it selects the non-matching lines hence
grep -vl 'pattern' ./*
prints the name of each file that contains at least one line not matching 'pattern'.

So, note the difference:

grep -L prints the file name only if there is no line matching 'pattern'
grep -vl prints the file name only if there is at least one line not matching 'pattern'

^1:
based on the above, it's easy to see when could these two commands produce the same output:
-either when the file is not empty and all lines match the pattern - in which case there will be no output
-or when the file is not empty and no line matches the pattern - in which case it will be listed

Moral of the story: never use grep -vl to emulate grep -L.
If your grep does not support -L, this is the proper way to emulate it.

As an extra note, on systems whose grep doesn't support the -L option (a GNU extension), using -vl wouldn't help as @don_crissti has shown, you'd need to resort to a shell loop. The equivalent of

grep -L pattern ./* 

would be:

for file in ./*; do { grep -q pattern || printf '%s\n' "$file" } < "$file" done 

You'll notice that the redirection is done on the whole {...} instead of just grep as we don't want the name of the file to be printed if it can't be opened.

For the equivalent of grep -ZL pattern ./* (which you need if you want to be able to post-process that output reliably), replace %s\n with %s\0 above.

For the equivalent of GNU's grep -rL pattern ., you can do:

find . -type f ! -exec grep -q pattern {} \; -print 

Though it would also print the names of the files that are not readable (the -readable find predicate could be used, but it's also a GNU extension, so chances are that if your grep doesn't support -L, your find won't support -readable either).

With zsh:

for f (./**/*(DN.)) {{grep -q pattern || print -r $f}<$f} 

Let's use a formula to represent each combination of options.

• There is a file with n lines
• The text in line i is represented as L(i)
• match(L(i)) means L(i) matches a search pattern

-l: A file with at least one matching line

-L: A file without any matches

-vl: A file with at least one non-matching line

-vL: An empty file or a file where every line matches