Good call, for an equity only position it is a huge upfront risk, and 4 years to vest is a long time for that risk to mature. If it where me, I would not take a pure equity stake without some ownership after a 30 day trial window. Maybe not the whole thing, but I would certainly want ownership of my entire stake within a 12 month window. The thing to remember in a pure equity arrangement is that you should be treated equally to the other founders after consideration has been made for the efforts put in up until you enter the company. If it is ground floor and no work has been done your equity and vesting should look like their equity and vesting, if it does not then you should consider that a red flag.
As for the consultant title, I don't think it is a big deal until salary is involved, they are probably not wanting to carry employees on the books as their are all kinds of legal situations that arise from doing so, standard (I am not a lawyer disclaimer applies). For example if you are not drawing a salary then how do you comply with minimum wage for a w2 position, that is just one of many, it can be done but it takes effort to dot all the i's, there is a lot less to deal with if everyone is a consultant, and responsible for themselves legally. I have been part of several efforts where we where all S-Corps and had a blanket LLC that each S-Corp or consultant held ownership in, while it is not totally the norm, it is not unheard of. What does the other founders structure look like? Are they employees or are they consultants as well?
The bigger question is does your equity place you on the board of directors for the company? If it does not then you may want to consider carefully your position in the direction of the company and you ability to direct that direction.
Also, 4 years is the standard for vesting, not 12 months.
It sounds like these guys may have bad lawyers.