They have had Verizon and ATT for a long time, the others are new.
If you can find it (they don't have it on the website) their terms and conditions say you are not supposed to tether or use a phone as a hotspot. They have no way of knowing the difference, but if you are on the phone with them and tell them that you tethered, they will cut you off, until you pay for a new month. They are a Tracfone subsidiary and the same folks work both customer service sides, and it keeps training to a minimum. And believe me, training is at a minimum.
That said, I have been using a smartphone this way for several years. But if you buy one from Straight talk, there is a 50/50 chance that the hotspot feature has been disabeled. I know some LG models of theirs do work, and my unlocked Motorola phones work well.