Yes, appearing students can apply for VITEEE and JEE Main exam 2018.

You can check the eligibility criteria of the exam below

VITEEE

- You should have secured 60% marks in Physics, Chemistry, Mathematics/Biology taken together in 10+2 or equivalent exam

- Candidates belonging to SC/ ST categories and North-East should have secured an aggregate of 50% marks in Physics, Chemistry, Mathematics/ Biology.

To check the complete eligibility criteria you can refer below link

https://engineering.careers360.com/articles/viteee-eligibility-criteria

JEE Main

- You must have passed 12thclass or qualifying exam in 2016 or 2017. Appearing students can also apply. 

- For admissions to NITs/ IIITs/ GFTIs, candidates should have secured at least 75% marks in class 12th exam or be in the top 20 percentile in the class 12th exam conducted by the respective boards. For SC/ ST candidates, the eligibility criteria is 65% marks in class 12th.

To check the complete eligibility criteria you can refer below link

https://engineering.careers360.com/articles/jee-main-eligibility-criteria

Good Luck!!