Do you mean that the statue or intention of congress was unclear or that it doesn't matter whether it is an article III court or not?
There is a tremendous amount of evidence that congress intended the FISC to be an article III court. Objections were raised specifically on the basis that it would extend the judiciary into policy making or not be a constitutional valid subject for an article III court.
Several courts since the 1980s have considered the claim that it is not an article III court and have rejected the argument every time it has been raised. (see United States V. Megahey or the second circuit appeal)
I think it is an important question for a couple reasons:
1) the minimization procedures that the court must approve are an extension of the warrant power that the court is granted to satisfy the fourth amendment.
2) the warrant power itself is generally understood to require a judge where a warrant is required in the first place(see keith 1972). Of course, there are cases where it is possible that an independent officer(not a judge) can satisfy this requirement but it is difficult to see how judicial oversight can be excluded in this case.
3) congress intended (by the committee reports) that judicial oversight was the only valid means by which the executive could be checked. Simply requiring documents wasn't enough for congress.
EDIT: reply to below
I understand the requirement that the constitution sets out for judges to apply to them specifically and not to any individual court. Thus temporary courts or tribunals(composed of judges that were appointed to other courts) can act as a proper article III court.
In terms of the subject matter of article III courts the constitution says that: "The judicial Power shall extend to all Cases, in Law and Equity, arising under this Constitution, the Laws of the United States, and Treaties made, or which shall be made, under their Authority;" I don't think it requires that every court necessarily can consider all cases that the judicial power is entitled to hear; it only acts as to set out what the maximum subject matter that a federal court can consider. There are other courts like the FISC/FISCR that also have limited subject matter jurisdiction under statute such as the United States Court of International Trade that only hears customs cases yet it also an article III court.