Is this accurate

Yes; millions of Indians served in the British Indian Army in WWI, virtually all of them volunteers

were they appreciated as front line forces or chai boys?

Frontline forces; Indian Corps served with distinction on the western Front from 1914-15, especially at Nerve Chappell where the Indian memorial is located today. Indian Cavalry fought with distinction on the Western Front, notably with the (temporary) capture of High Wood, during the Somme Offensive, July 14-15th 1916. Most of the British Indian forces fought in the Middle East, and were the backbone of the forces facing the Ottoman Empire.

...'colonial' forces made up to a third of soldiers in the BEF during the first WW. Is this accurate, [?]

To some extent. Initially the long-service volunteers of the British Indian Army were, other than the 120,000 regulars in the BEF, the only trained regular soldiers available to fight the German Army in France and Belgium.

Upon the declaration of war two infantry divisions (the Meerut and Lahore) and one cavalry brigade were mobilised to France in September 1914 totalling some 140,000 men. 90,000 soldiers and cavalry and 50,000 labourers.

If these numbers are correct, the men of the British Indian Army deployed to France in September 1914 outnumbered the British native regulars by 20,000. This was to change as casualties of the British Indian Army mounted and Kitcheners' Volunteer Armies became available.

and/or were they appreciated as front line forces or chai boys?

I'll quote David Omissi for this because I think he gives a good account of why the Indian sepoys were so important at the outbreak of war:

"That the Indian Corps was ultimately deployed in Europe ... was decided by the flow of events during their transit. The was in the west rapidly descended into an series of almost daily crises and reversals for the French, British and Belgians. The German war plan - the famous Schlieffen Plan - appeared to be unstopable and the Kaiser's army nearly invincible. Fortresses designed to halt armies were either bypassed or crushed [...] What mattered now were not fortifications but men and their rapid deployment. What Britain needed from it's Indian Army in 1914 was simply men - to hold lines, plug gaps and halt German assaults with rifle fire and bayonets."

The British Indian Armies first battle was at Ypres on the 22nd of October during each armies frantic assaults and attempts to outflank one another during the 'race for the sea'. Their first Victoria Cross was won on the 31st of October by Sepoy Khudadad Kahn for manning a sole machine gun in the face of a German attack until his position was overrun and his comrades were killed. He was wounded and hid under a pile of bodies until he could crawl back to his regiment after nightfall.

I'd argue that these are the actions of a highly trained, front line army. The award of a Victoria Cross* to a sepoy (private) within a month of their first battle is proof of their 'appreciation'.

*certainly not the only one awarded.

A little off-topic but I think it's interesting to note that describing the army as 'Indian' is inexact. Colonial India encompassed modern day India, Pakistan, Burma, Afghanistan, Nepal and Tibet. The 'martial races' theory that led post-Mutiny recruitment meant that the new Indian Army would be made up of Sikhs, Dogras, Jats, Punjabi Massalmans, Pathans and Gurkhas. Men from areas now not totally in modern day India.

I hope this was what you were looking for; This is my current dissertation topic and I'd recommend these books if that's OK?

• The Worlds War: Forgotten Soldiers of Empire by David Olusoga. (Head of Zeus, London, 2014) His BBC documentary is very good too.
• Sepoys in the Trenches: The Indian Corps on the Western Front 1914-15 by Gordon Corrigan. (Spellmount, Gloucestershire, 2015)

Thanks for your excellent answer mate!