Yes, you need level 1 of Lockpick and Pickpocket to join the thieves guild. At least Pickpocket can show up on equipment as a bonus, so you may want to keep an eye out when trading or selling off loot, etc. I found an amulet with a Pickpocket bonus before heading to Verdistis, and a belt after that. I don't recall if Lockpick can be an equipment bonus; I maxed that skill (you can get 2 levels in the thieves guild), so would not have paid much attention to that bonus if I saw it after that.
If you want to cheat and just get these skills temporarily,
iZakaroN's SaveEditor (or from
Kiya's site, with description) can be used to unlearn skills (among other things).
