No. While "merger" can be used as a mass noun, that is not the way it is being used here. In this sentence it is being used to describe one particular merger, and so it is being used as a countable noun. Thus an article is required.
In general, when a word has multiple definitions or multiple uses, the rules that apply when you use that word in any given sentence are the rules that apply to the particular definition that you are using. To take an extreme example, "Bob" can be a verb meaning "to move up and down" and can also be a proper name, short for Robert. You wouldn't say that because it should be capitalized when used as a proper name, that therefore you should capitalize it when using it as a verb.
By the way, in this case, "merger" as a mass noun is pretty much only used in that one particular phrase: "ripe for merger". Occasionally someone will say "there is a lot of merger activity in such-and-such industry" or similar phrases.