In the adjective sense, those are the same words as alternative spellings. The one without a hyphen is more common in computer-related cases, such as "an inline function", while the one with a hyphen is, in my experience, more common in mechanical or manufacturing situations - "in-line engine", "in-line manufacturing".

Is in line correct?

But when it comes down to waiting on line versus in line, the distinction is regional. According to Google Ngram, in line is used considerably more often than on line. In the 2003, the Harvard Dialect Survey reported 88 percent of respondents nationwide use in line.

Which is correct inline or in line?

Explanation: “In line” tells where and is an adverb: “Bob is in line to receive a raise.” “Inline” tells what and is an adjective: “Bob enjoys inline skating.” Solution: Use “in line” when you want to indicate where something or someone is.