Are other pirates than the strawhats able to find raftel?
According to the plot, Nico Robin is hinted to be the only person alive that can read Poneglyphs. This is why the World Government declares her to be a high priority target. Source from Wikia

That being said, we've seen two other potential ways for Poneglyphs to be deciphered:


The Voice Of All Things is what Roger used to understand the Poneglyphs and reach Raftel. It is known to be an extremely rare ability, but we have already seen a couple of other characters exhibit it, including Luffy. However, the purpose of this ability isn't to read poneglyphs and even those with it may not be able to use it in the same way.
The Three Eyed Tribe is supposedly able to decipher Phoneglyphs with their third eye. This is why Big Mom had a daughter, Pudding, with a member of the tribe. However, it isn't clear if she will be able to activate this power, since she is a mixed type. We don't really have information on other members of this race, but considering what the World Government did to Ohara, it is possible the three eyes may no longer be around.


So the answer to your question is yes, based on the information we have so far, Robin is the only one who can decipher them. Hence it might be true that only the Strawhats can figure it out in the end. However, other pirates can always use underhanded means to get this information from her.