Do you need your Ranger tab to get into a Ranger Regiment?

For you right bow, no. But they will require you to get one before you see SGT or they will send you down the line. I've seen guys get RFS after their first failure and I've seen guys that were given 3 chances at Ranger School. I guess it's who you know in that regard.
If you try to go later in your career as a SSG to RASP 2 they wont even look at your packet without the precious.

The short answer is no. Longer answer is that it depends on your MOS and rank. Rangers in the support companies aren't required to have a Ranger tab (although they still need to attend RASP) however, having a tab as an NCO in these support companies is highly encouraged. As far as I know, soldiers in the line companies (infantry) are required to have a tab to be in Ranger Regiment. My husband is a Ranger and this is my understanding of the way it works from his explaination. Hope that helps!

You don't need it to go to RASP and get into Regiment. You will need it to remain there. I was RFSed after one failed attempt at Ranger School. They were downsizing at the time. Sometimes guys get multiple tries. It also depends on your MOS, and which company you're in. On the line, you can get your SPC without it, but you'll still be addressed as and respond to "Private." Normally you can't get promoted past that. I've seen it, but only with a guy who had been to the SF version of BLC in the SFQC and eventually hit his TIS and TIG requirements to promote automatically. Otherwise you have to get the Tab to even be called a SPC. But, off the line, like in HHC, I've seen Corporals and maybe a Sergeant 11B without the Tab. I knew a POG who went from SGT to SSG without his Tab.

If anyone cares, I've seen plenty of guys in RASP 2 without the Tab. Some even made it into Regiment. There were several Ranger Officers in SURT with all the Joes, and some NCOs as well.